Well the title says most of it but I'll give a bit more detail about my preferences here.

Previous RPG's played :3.5 and 4th ed DND

DnD chars:

3.5 ed: Septimous (human shadowcaster, quite ruthless and reflective)

4th ed: Asul(shadar-kai warlock: star pact, Taking ruthless and reflectiveness to the extreme)

40k armies: tyrinids, necrons, thousand sons

fantasy armies: Vampire counts and dark elves

chaos god of choice: Tzeentch

Play style: I like quite philosophical campaigns but still want some combat to provide tension and cool mental images.

I think it is just a matter of personal prefferance. But personaly i would start with Dark Heresy. Do you have a GM? Are you going to be running the game? If so what are you the most intrested in?

No i do not currently have a GM but i know a few people in my local GW(boston in England) who participate in TTRP. To start of with i would probably want to be  a player as it's genrally a bit easyer for someone less well versed in the rules.

Hey there, welcome to the forums!

As has already been said, it's mainly a question of personal preference - a mixture between what kind of characters you like the most as well as what kind of playstyle and agenda you find most interesting.

Basically, it goes like this:

• Dark Heresy: Groups of loyal Imperial servants from all angles of life, inducted into the Inquisition to hunt down traitors and heretics.
  Theme: Crime/Action
  Basic elements: combat, investigation
  Comparable P&P: Call of Cthulhu
• Rogue Trader: A Lord-Captain, his very own capital ship and his capable command crew, traversing the void in search for riches and relics.
  Theme: Space Opera
  Basic elements: combat (ground and space), diplomacy, exploration, trading
  Comparable P&P: Traveller
• Deathwatch: Space Marines, the Emperor's mightiest warriors, fighting against the alien horrors that threaten entire worlds.
  Theme: Heroic Action
  Basic elements: combat
  Comparable P&P: Exalted

Pick the one that would interest you the most and go from there. Given that they are all somewhat interesting, you will likely soon find yourself "branching out" into the other books either way. All the RPGs intermingle with each other on some level, and though I would not recommend crossover games, you can still transplant elements from one into the other, to a certain degree.

Hope that helps! In case you have any more questions ... these forums are pretty active, and you'll surely have them answered here.

Personally I go with Dark Heresy.  There are so many factions and ideals that it would be right up your alley.  Last game I had my tolerati scum (think voodoo) and a cleric with radical beliefs had a excellent conversation about aliens.  Then again we were alone and at ascension level.

Thank you for your recommendations. I think I will probably go with either dark heresy as it seems to deal in the myriad shades of moral  grey I like to RP within. Or as a possibility I might try black crusade if it receives a good response by forum goers as RPing a chaos sorcerer would be fun.

In terms of complexity, the games follow the order of release. Dark Heresy is the simplest, Deathwatch the most complicated- in terms of game mechanics, at least...

I think the best thing about Dark Heresy compared to the others is that the system is the most 'theme neutral'.

Whereas Rogue Trader has Endeavours and Achievement Points and Deathwatch has Renoun, and both of them are essentially cashless and both have game/theme specific psychic powers etc., Dark Heresy doesn't have these features making it more flexible.  You can build any type of adventures you want.

And if you do play it as intended, who doesn't like burning heretics?

And yeah, posting in the Black Crusade forums is heresy!  ZAP ZAP ZAP!

Hopefully, BC will bring the most neutral system, getting ridden of classes, it would be possible to create any character (and I hopen not only chaotic ones).