I'm currently looking into a Chaos Space Marine codex army. As such, I'm going to be looking into the units the chaos codex has to offer.
Pros: lots of melee options. Not a BAD melee statline; 3 attacks, options in terms of melee weapons. He can pick up speed, or armor.
Cons: Daemon weapons, while having some cool abilities? Only one's really that useful, and getting the most out of a Nurgle daemon weapon involves going toe-to-toe with stuff that can probably insta-kill you. Slaaneshi daemon weapons would be cooler if everyone wasn't immune to instant death, and Khornate weapons crap out on you 1/3 of the time. (the other 2/3 it's a metric shit-ton of attacks, though....)
Overall? I'm a bit 'eh' on him. The bargain version takes lightning claws and a mark, and it's not bad. It's not necessarily great, either, as all you get from him is a CC unit.
Pros: Psychic powers. Melee stats close to the Lord's (WS5 vs 6). Enables the almighty Lash of Submission, though with Warptime he's pretty capable in melee vs. troops.
Cons: Not a lot of interesting psychic powers outside of Lash and Warptime. Doombolt? Seriously? Bolt of Change is alright but not a substitute for melta. Gift of Chaos is laughable. Winds of Chaos has potential, but you should be able to get flamers to do it for you.
Overall? Lash or Warptime have my bids so far.
Pros: Nasty melee statline. 4 attacks, WS7, S6. 3+/5+, 4 wounds.
Cons: easy to pick out with shooting.
I'm tempted to slap wings and a mark of Nurgle on it for a 150pt guy with 3+/5+, T6, and a jump pack and the ability to fly and smash things. If I got a psychic power, I'd go warptime or Lash..
I have seen him used as a cheapo fire magnet.
I think if I ran 'em, I'd run at least two and bring some defilers for the large-target thing, and run 'em behind Rhinos. That might see them into melee. Additionally, I think that melee support might be useful in a Slaanesh-heavy list.
Kharn the Betrayer
Pros: Abject nastly in melee.
Cons: Occasionally kills your own guys. NOT immune to instant death.
How do you use him? If you want a CC HQ choice, he's pretty cost-effective in terms of lethality. You hide him in a squad, and split him off like a homing missile into a squad that doesn't have a powerfist. As long as you avoid something that can insta-gib him (or that he can kill before it can, like Dreadnoughts with his S6+2d6 on the charge) he's going to bring the pain.
Lucius the Eternal
Pros: He packs a Doom Siren and a neat ability to hit people back who hit him in melee, and knocks an attack off the other guy. I6 doesn't hurt, either.
Cons: Not immune to instant death.
Honestly, I see a chaos lord with a Doom Siren and the whole 'Armor of Shrieking Souls' going for it. Falvorful? Yeah. Doom sirens are nasty, but unless it's themed? Kharn's still more capable, as Kharn cranks out about 6 hits in melee a turn to Lucius'....2-3?
Pros: Nasty weapon selection; powerfist, power weapon, heavy flamer? That's respectable, and warptime on top of that doesn't hurt.
Cons: Not immune to instant death. Fairly pricy at 170.
Overall? He's not BAD, but he doesn't jump out and scream 'take me.'
Typhus, Herald of Nurgle
Pros: Force weapon, daemon weapon, and he's just abjectly destructive up close. He's also absurdly resilient to non-power weapon, non-instant-death stuff between 2+ armor save and Feel No Pain.
Cons: 225pt price tag. There's a lot of other stuff you could get for this, like 3 Obliterators.
Overall? I like the lethality. I don't like the price tag.
Pros: Can get your regular marines Fearless and +1S at 3pts a head. He's durable and packing an isntant-death weapon, but still allows armor saves.
Cons: He's not actually that great in melee. He's expensive, and only makes your rank-and-file troops cost more while sometimes killing 'em off. And did I mention, no invulnerable save?
Abbadon the Despoiler
Pros:...what do ~7 S8 power weapon attacks at I6 that re-roll wounds feel like to you in melee?
Cons: PRICE. 275 points for this squad-killing brutality. He falls prey to 5th's rules on assault...Abby goes in, Abby cleans the squad out, Abby consolidates? Abby gets shot to hell and back. Terminator armor only goes fo far.
Additionally, you have to get him to the fight; Deep Strike gives them a turn to nail you and the Land Raider approach...relies on a Land Raider.
Reflections on the HQ choices
Kharn's the nastiest melee solution.
If you want footslogging template death, or just general control, Lash Sorcerors are the most versatile choices.
Daemon Princes are potentially nasty, but I think you have to be very conscious of the build. They're going to be fire magnets, but Chaos-Zilla (2 DP, 3 Dreads, 3 Defilers, some rhino troops) gives you enough targets to pull it off.
The named folks are otherwise damned expensive, but I think they might have their uses.
If it's not Kharn, a sorcerer, or a DP build? I think I'd try to spend the least on one, and I'm looking at a Warptime Sorcerer as about the cheapest it gets.
The Marks of Chaos
I think it's worth mentioning the marks of Chaos early on, as they're available to damn near everyone, and either they're built intothe Cult Troops or you can take 'em on top of the Chaos Space Marine statline.
Mark of Tzeentch
Your guys get a 5+ invulnerable save. To be honest, I think this is about the least useful mark. If you're going to take heavy AP3 gunfire, you should be in cover. People are used to forcing enough 3+ saves to kill you, so to be honest you're probably not going to see a ton of use for it.
On Terminators and ICs, though, it kicks the invlunerable save up to a 4+, which makes them a bit more durable. Still, the mark of pretty pricey.
Mark of Nurgle
Go to T5. unless it's for purposes of Instant Death. This is pretty much the most costly mark you can take. At ~50pts, it ups the basic Chaos Space Marine's cost to 20pts if you take a 10-man squad.
I won't lie and say that T5 makes you more durable. On the other hand, if you take 2-3 squads with the mark of nurgle, you can buy another squad. If you're going to put it on tacticals, you should think about Plague Marines instead.
Plus, if you lose the icon? OW. That's a lot of pain to deal with any way you cut it.
Mark of Slaanesh
Go to I5. I6, if you're an IC. Honestly, this one sees the most play against fistfighting other marines. The average loyalist tactical marine isn't a CC threat. Space Wolves, on the other hand? They'll try to crunch your face in with CC and they CAN DO IT. Helpful against that, but it won't make a lot of difference otherwise.
Mark of Khorne
I think this'll get you the most mileage per cost. The average marine now has 3 CC attacks; base 1 + 1 for MoK +1 for pistol/CCW. You have lots of dice to throw; and you have a decent chance of beating down Ork Boyz.
Downside? Gotta get into assault to use it.
Mark of Chaos Glory
Cheapest icon. Re-roll leadership tests. Good for what it does.
Overall on Icons
Right now, if I take basic chaos marines, it's going to be either sans icon, Chaos Glory, or Khorne. Khorne goes well for the powerfist + 2 special weapons rapid fire and recieve-the-charge strategy. Slaaneshi marks are ok, but of limited use. I4 to I5 just isn't that great. Nurgle and Tzeentch are bloody expensive...