This is a question I've pondered some, and so far I've gone with Crisis Suits over Stealth suits. But, I think it's time enough for me to poke at the alternatives. I'll start with the battlesuit's common ground, then move to what sets them apart.
Battlesuits in general have a 3+ armor save. Obviously, this beats the pants off Fire Warrior armor at 4+, carapace at 5+, or Kroot hide at 6+ or nil.
Suits are also jump infantry with jet packs. As such, they have a 6" move in the Movement Phase and a 6" move in the assault phase. As such, suits can get a decent movement during a turn, or jump in and out of cover.
The other benefit of suits with movement? They can fire rapid-fire weapons as though standing still. This applies to the Crisis Suit more than the Stealth Suit, as the Stealth Suit's guns are all Assault weapons. Both suits have the natural Tau BS of 3.
Finally, suits have Acute Senses, which grants them a re-roll on Night Fighting Rolls. Not bad, but useful only every so often. It applies more to Crisis Suits anyway, since they have weapons with a range better than 18".
All battle suits may of course Deep Strike, but the best deep-strike enhancement Tau can get is a re-roll on the scatter dice. I'd rather skip it, to be honest.
The Stealth Suits
Stealth Suits are 30 points a head; 3-6 per unit. For this, you get S4, the 3+ armor save, the jump pack, and start out with a Burst Cannon. Every third suit can take a Fusion Blaster at 2 points more. Each suit may take the same support system, or you may upgrade the leader (at a cost of 5 points) to get access to the armory. If you really want to, you can make that a +10pt leader upgrade to give him WS3 over WS2, and I3 over I2. I don't see a point in making him the Shas'vre, as you don't need hte extra WS. You may buy a markerlight on either leader-character for +10 points.
The big perk of the Stealth Suit is, surprisingly, the Stealth Field Generator. If they want to shoot you, they 'spot' you on 2d6x3. Barrage weapons roll an extra d6 for scatter. So, in short, the average distance you'll spot a stealth suit at is 21 inches, as 2d6 averages a 7, and 7*3 = 21. Stealth Suits may infiltrate in addition to their outflank, but that does put you potentially closer to the enemy.
The con is that the Stealth Suit is inherently short-ranged and mono-tasked in terms of weapons. Burst Cannons are only useful for harming infantry or potentially monstrous creatures. You will have to skirt the edge of your natural Stealth Field range in order to jump-shoot-jump, which may or may not backfire on you. If you do want the Fusion Guns, you are getting well within the range of your Stealth Field being ineffective.
An alternative use for a Stealth Suit Team is as a markerlight squad. Kept cheap, you can take a minimal 3-suit squad with a team leader, markerlight, and a couple of marker drones. This would cost you 165. You get three BS3 Markerlights for 165 points. It's expensive, but they are harder to engage because of the stealth field.
The Crisis Suit
The Crisis Suit is the bigger, burlier cousin of the Stealth Suit. It is S5 and T4 with two wounds, which is a significant upgrade in durability over its cousin. However, it loses the stealth field (big surprise there.) Each suit is 25pts naked, and teams are 1-3 suits per elite slot.
Crisis Suits have 3 'hardpoints' that you must fill. Each weapon is one hardpoint, and each twin-linked weapon fills 2. Each support system takes up a hardpoint. Team Leaders or Commanders can take hard-wired systems, which do not occupy a hardpoint.
If the last paragraph didn't clue you in, the Crisis Suit has lots of options. The multi-tracker allows suits to fire two weapons instead of one. For 5 points, it's a sweet deal.
So, on to Crisis Suit weapons. They can take flamers, fusion guns (S8, AP1, 12" melta), Missile Pods (Assault 2, 36", S7 AP4), Burst Cannons (S5, AP5, Assault 3, 18"), or plasma rifles (S6, AP2, 24" Rapid Fire). Note Crisis Suits may fire Rapid-fire weapons as though they had not moved.
The Crisis Suit is just about your only source of middle-weight fire. You should pretty much always equip them with a missile pod. Missile pods are your light anti-armor weapons, or they readily wound just about whatever you point them at. They also have a fine stand-off range. When you look at the rest of the codex, your guns move from S5 (virtually everywhere) to S10 AP1 (Rail Guns on the Broadsides and Rail-Heads).
The Crisis Suit Missile Pod is the only way to bridge this gap, and it's an excellent multi-role weapon. As such, they're pretty much mandatory when it comes to kitting out a Crisis Suit. Otherwise, you're relying on Railguns for every last anti-tank shot in your army, which means you'll have to spend them on Trukks and Land Raiders alike. I cannot stress enough just how useful it is to give your Crisis Suits these weapons.
So, on to the rest of the hardpoints. You can always twin-link the missile pod, but then you're basically committing to a flamer or support system, since you can only shoot one weapon if you take a twin-linked one. Why? There's the whole '3 hardpoints' thing, and you're taking up two. Your other gun is something you can't use with the pod, so you could go for the support flamer. Such a configuration IS cheap; TL-Missiles + Flamer = 47 points; not bad for a suit.
You could equip a burst cannon to the suit, but that's useful only for anti-infantry fire, and up close. With Tau, your army is pretty much S: Crappy, WS: Laughable, and I: goes last. So, screening units, distance, and other countermeasures to melee are your buddies. Crisis Suits can theoretically do ok in melee against S3, T3 folks, but even then you're losing the use of all the guns you paid for. If you can range a burst cannon, they're close to you, and the best you'll be is 24" away the next turn.
The flamer, though? Last-ditch weapon. You get one good shot to BBQ hordes. It's cheap, but you pay for what you get. Flamer + Missile launcher combo = can hunt light-weight armor, and has a last-ditch point-defense weapon. If it fails, your suit WILL be in assault range, and you know what happens to Crisis Suits in assault.
I personally favor the plasma rifle. S6, AP2 wounds you and only lets you have cover saves. It also negates crap like Feel No Pain. It also hunts monstrous creatures. And, if stuff like Marines, Terminators, (including Plague Marines) or Carnifexes get close to you? You will be glad for the AP2. Something like a Burst Cannon will just annoy it.
Let's do the math...team of 3 suits, BS3, with point defense weapons. At 24 inches, you get a plasma rifle shot and no other gun. Obviously, the plasma rifle wins here.
3 Burst Cannons = 9 shots at 18", 4.5 hits on average.
Vs T6: 1.5 wounds; 0.5 stick after saves.
Vs T5: 2.25 wounds; chances are there's a 3+ save involved so 0.75 wounds.
Vs T4: 3 wounds; if it's a 3+ save you get one, if it's a cover save you get 1.5 kills.
Vs T3: 3.75 wounds; likely 4+ save so you get 1.875 kills
3 Plasma Rifles outside of rapid-fire range = 1.5 hits.
Vs T6: 0.75 wounds; usually no saves.
Vs T5: 1 wound; cover saves if applicable reduce to 0.5 wounds
Vs T4: 1.25 wounds; 0.625 if cover saves apply
Vs T3: 1.25 wounds; 0.625 if cover saves apply
3 Plasma-Rifles in Rapid-Fire Range = 3 hits
Vs T6: 1.5 wounds; usually no saves. PAIN
Vs T5: 2 wounds; cover saves reduce to 1
Vs T4: 2.5 wounds; 1.25 if you have cover
Vs T3: 2.5 wounds; 1.25 if you have cover
What can you take from this math-hammer? At 18-13", the Burst Cannon is a bit better at killing infantry, but the Plasma Rifle will always beat the Burst Cannon against monstrous creatures and things with Feel No Pain. Once you get into rapid-fire range, the Plasma Gun beats the Cannon outside of cover, hands-down. Against T5 and T4 targets, the plasma gun beats the cannon in rapid-fire range. T3...cannon still wins a bit on volume of fire, as both wound on 2+ by now.
Flamers probably win against well-packed enemies with no armor saves, but the issues of employment get 'em a bit. The Plasma takes on a lighter anti-armor role, but AP2's benefits against Feel No Pain, Monstrous Creatures, and armor beat the silly AP5 of the Burst Cannon. Plus, you get another 6" of range, which translates to more shots.
Crisis Suits vs. Stealth Suits
So end of the day, we've got two different roles for an elite slot. Stealth Suits are pretty much anti-infantry only, though they can risk themselves to get anti-tank shots with meltaguns. Alternatively, they can bring in a few well-defended markerlights (that...average 1.5 light hits for 160 points.)
Crisis Suits, on the other hand, are about the only thing that can give a Tau army middle-weight fire. Simply put, there are lots of sources for S5 fire in a Tau Army, including:
-Devilfish (seven shots)
-Hammerhead SMS/Burst Cannons (4-6, plus any submunition shots)
-Fire Warriors (in a pinch)
-Pathfinders (also in a pinch)
-Anyone that can carry gun drones (read: Piranhas)
There are just lots of sources for anti-infantry fire in the Tau army. So, where can you get middle-weight strength fire from the Tau Army?
-Seeker Missiles (...which involve bringing a hefty amount of Markerlights, and keeping something like the Skyray Alive)
-Hammerheads with Ion Cannons instead of Rail Guns (Yes. Your opponents wil thank you for taking less railguns)
Bottom of the line? I think Stealth Suits can do the damage, but the Crisis Suits can fill a niche in your army that, well, no one else can. Fill an Elites slot with a Stealth Suit is an opportunity cost; you could've gotten a Crisis Suit instead.
When you look at anti-tank in a 1500-1850 Tau, you can probably fill your heavy support section with 3-4 Rail Guns. They're either BS4, or twin-linked BS3. Maybe a few meltaguns in there on Piranhas, that can deliver them. Past that, it's a matter of either getting some S7 missile lovin' on the Crisis Suits, or more anti-infantry power elsewhere.