As a lot of folks are figuring out, the vet guard squads are a hell of a troops choice. You can kit 'em out in a variety of ways, and there are the doctrines as well. At least the 'doctrines' are a nod to the old codex.
Squad gets camo cloaks and defensive grenades. If the squad's going to sit and shoot, they might as well take this and be a pain in the ass. Throw them a heavy weapon, and perhaps a special or two, and you've got a squad that'll be a pain to dislodge unless you ignore cover with your shots. A BS4 Lascannon in a squad, and a plasma gun or two at best is kind of disgusting.
Everyone in the squad gets meltabombs, and someone gets a demolition charge. At this point you've kind of decided that you don't want the squad to live. You've probably given them meltaguns, or flamers, because you want short-ranged weapons to get the demo charge off. I mean, you're going to try to out-and-out obliterate something with the demo charge, and a couple of flamers will help it out and keep the squad cheap.
However, the meltabombs...not as useful. You already have frags and kraks. Meltabombs are more of a consolation prize. If you're going to make the squad use 'em, they're on an anti-armor mission. So, you're hopefully bringing those meltaguns. Thing is, you're firing meltaguns at a target. If that doesn't nuke it, you're shooting meltaguns at it again. Then, you have to assault the target to slap meltabombs to it. Well, believe me when I say it's hard to get assault support in there outside of non-open-topped, non-Land-Raider vehicles. You have to roll up, and wait a turn before you pile out and assault it. Now, if you've got meltaguns, you want to roll up and shoot those. It's just not going to work out well.
Everyone gets a carapace armor, and thus a 4+ save. It's annoying, to be sure. It makes a squad more liable to survive their Chimera going Kaboom, but it DOES add 30 points to the price tag. It's almost half again the cost of the squad; the guys go from ~7 a head to 10 a head. I think the biggest benefit is that your enemy must devote more shooting to the squad. Most troops carry AP5 guns, and suddenly the average tactical squad or dire avenger unit can't just evaporate a squad caught in the open.
Camo cloaks for staying in place and getting a BS4 heavy weapon.
Demolitions...only if you really want that demo charge, and to REALLY write off that squad.
Grenadiers...perhaps if mechanized. Perhaps.
The role of the vets
If mechanized, vets serve best as a meltagun delivery system. 100 points for three BS4 meltaguns? Yes, please. I think we've all covered just how nasty and versatile a triple-melta vet squad is in a Chimera with multi-laser/heavy flamer. That's also a bit why you probably won't see so many 2 flamer/heavy flamer vets. The Chimeras can bring the heavy flamers, and you ARE kind of wasting BS4 on template weapons.
If standing still? Forward Scouts and a heavy weapon, perhaps plasma weapons to taste. Or, maybe take a flamer or two since they're cheap and it gives you a little counter-push. 120 gets you 10 vets, camo cloaks, an autocannon, and two flamers.
Platoons will get you heavy weapons cheaper. You must take a single command squad at 30 points (and perhaps a Chimera or heavy weapon). There's really no point in kitting out the 5 guys in the command squad with much, since there aren't many bodies to soak wounds or guard that heavy weapon team, and it's ld8 unless you've got a Commissar.
The Platoon Command Squad (1)
Cheap. 30 points for 5 guys; one gives orders. The Platoon Commander has a 6" command radius, and three orders (and it can give one a turn).
'First Rank Fire! Second Rank, FIRE!' gets lasguns another shot. Most useful if you're dealing with combined squads. Move up, flame something and crank a lotta shots; hope you kill it.
INCOMING! lets you go to ground immediately for +2 to the cover save instead of +1. Squad is now annoyingly durable, and...not shooting. Situational at best. If you can combine it with a commander's 'Get Back in the Fight!' then it helps a bit.
'Move! Move! Move!' is a run move that lets you take the highest off 3d6. This one's useful for grabbing objectives.
So, with these orders in mind...you've got to keep the command squad close to the platoons if you want to use them much at all. However, these orders are neat, but not THAT essential. They're all pretty situational, and it really means you can hide the command squad if you want. They'll get you a Chimera you can use to add fire and counter-attack with a flamer.
The Infantry Squad (2-5)
They're BS3 pads for heavy weapons. You have to bring two of them in a platoon minimum, but can get up to 5 per troops slot. Their job is to bring a heavy weapon, and with BS3, you have to keep in mind that volume of shots is your friend. Autocannons and heavy bolters are 10 points a head, so you can crank out shots and have a few stick. I'd take the autocannon for the range and its ability to engage just about anything shy of AV14. That means that Infantry Squads cost 60; 65 if you want a flamer in there as a 'just in case' thing.
Infantry squads can also mount up in Chimeras, and fire the heavy weapon out of the top. This is 115 for a multi-laser and autocannon, or move up and fire a heavy flamer. However, a 'stunned' result means neither the APC nor the squad get to shoot, but it lets you spam armor and score with it.
Infantry squads may also use the 'Combined Squad' special rule, which means you can throw any number of platoons together as a single unit. The pro? 'Bring it down' is more efficient; one order can twin-link multiple heavy weapons. The con? The enemy has fewer targets, and a successful assault can nail a LOT of guard in place. However, 35 gets them a commissar (and Ld9 Stubborn). If you could give that Commissar a powerfist, this would be more disgusting, but his potential S3 power weapon is......yeah, impressive. Sure.
The Heavy Weapon Squad (0-5)
In short? Skip it. 60 points for three models with 2 wounds, T3, and a 5+ save. This means in cover against handy-dandy S6+ weapons, there's a 50-50 shot you'll lose a heavy weapon. 90 points gets you 3 autocannons that are fragile. OR, 120 gets you two well-protected autocannons.
Special Weapon Squad (0-2)
35 points for 6 guys; three get special weapons. The job's simple: deliver special weapons. They can get flamers, sniper rifles, grenade launchers, meltaguns, plasma guns, or demo charges. Some uses that take their BS3 into consideration involve....
-50 points for 3 flamers
-65 for 3 meltaguns
-95 for 3 demo charges
Now, the special weapons squad can't take a transport, but the infantry squads CAN. However...these guys are vying for the job Vets have. Vets deliver more accurate meltaguns for 35 points more. Demo Charges might not hurt the chimera, but you MUST bring that Chimera in very close to the target. Flamers can be brought in Chiemras as well, but a squad of these in an infantry platoon can make a counter-push, I suppose. However, it's not hard to break this squad, since it's 3 guys with Ld7.
80 points for 20 WS2, BS2, Ld5 guys. Can go up to 50; each person is 4pts. For 50 points you can slap Chenkov into a Platoon Command Squad, and then drop 75 to give your conscripts 'Send In the Next Wave!' where you can sack the squad and bring in a new one. Per the entry, the conscripts move on from the controller's board edge, which probably precludes a bunch of crazy shit like giving them outflank with Creed.
Unless they're close enough to Chenkov to get Stubborn AND pass Ld5 tests for losing combat, conscripts are just a speed bump.
The Use of the Infantry Platoon
A minimal platoon costs 130, with two infantry squads and the command squad. This can net you three Chimera, or two heavy weapons in the squad. For my part? I don't think that much aside from the Infantry Squad are worth it, as they're small, vulnerable, or not that effective. I suppose if you really wanted to deal with the fragility and space, you could spam heavy weapon teams with autocannons, but you best be prepared to watch them run off the board in short order. Or, slap them in Chimeras and hope you don't see a lot of 'shaken' results.