Space Wolf assault marine is what I'll probably start with. Knowing me though, it's only a matter of time before I try something else.

Devastator.. I shall cleanse these heretics and turn these xenos into mush !

Assault would be my first choice. Tactical, my second - which I'm likely to do quite a bit, depending on the tactical/strategic requirements of the operation.

If Chaplains were in at release, I'd be doing that A LOT.

Actually, with the confirmation that Raptors will be in for Chaos, if I make another character that's a loyalist Astartes, I'll probably go Apothecary or Tactical Marine. Simply for a change-up.

Tactical if they could be speced to Termies, or Devastator to unleash the fury of the Emperor!

Tactical marine. Mobile, semi-support fighter, keeping enemy busy.

Sanguinary Priest! (Blood Angels Apothecary)

I have to say I'm a MAJOR fan of fast attack units. I'd LOVED to play a bike marine (I'm working on an all bike army, it is about 80 bikes, Smurfs on a 10-speed is OP). But I don't think this game will work like that. So the next best thing is a jetpack, which I'm betting the assault marine will be getting early on.

Apothecary
No servant of the Emperor shall fall if I can help it.

if I try one of the 'ard 'umies, I suppose it'll be either Apothecary or Tactical Marine.