Depends on what kind of RP you're looking for.
For me the best RP factions are the Lane Hackers and Cryer Pharmaceuticals, they're logical additions to their vanilla ancestors without superheroes (Oh, well, Phate... ok).
If you're looking for quantity of RP, pick any faction, it doesn't matter much, everyone has to RP somehow, fortunately or not.
If you're looking for easy and liberal RP without much restrictions, pick Zoners or Freelancers, they have the least restrictions and the largest ZoI. Outcasts and Corsairs come after.
Depends on what kind of RP you're looking for...you may try Researcher ID and carry some stuff around if that intrests you...do alot Forum Roleplay about the stufff...take it to research labs...sell materials on black market...that's my input...
But yeah, Freelancing is what i first had intrest in...
Every faction has a lot of RP. Every single one. Join according to your preference for their particular style of RP.
Some factions prefer hardcore RP with dedicated command structures that you MUST follow in RP. Other factions allow freedom of any RP you like, because well.. that's what their NPC faction RP demands them to. Yet others RP ruthless pirates who prey on defenseless transports but run from organised house navy presence. And then other factions take the navy head on, eventually lose and come back for more the next day. Some factions are dedicated to trade and talking yourself out of any dangerous situation. And then there are the factions that let you be an inscrutable agent bent on saving their house of origin (or maybe even all of Sirius) from various unseen threats, both internal and external. At the very edges there are the alien factions which proliferate the most unusual kind of RP for a cause that even the faction members can only stab guesses at.
Or if you prefer complete freedom, you simply are a freelancer. If people throw down the cynical veil of forumlancing for a moment, they can easily notice the RP possibilities that each and every path you can take in Sirius offers. In the end it's not down to some magical "RP meter", but to what tickles your RP fancy.
Join Junkers. It's all about the individual. Not that much PvP, and your ZOI is: everywhere.
Very few idiot indies. Lots of nice indies. Good factions with good people like Congress .:j:. and [collectors].
Lane Hackers are good, not much out-of-server stuff, nice people and always place for new members. As you are in a pirate faction you will probalby interact with all kinds of players ( Freelancers, Police, Cooperations ) and the RP is good, but not to hard to learn.
The only other advice I can give you is : The amount of RP and PvP is determined by your actions, not the faction itself.
K then let me do some clarification. Essentially I am looking for the faction that offers the most in-game conversation. I am already a semi-member of the Xenos Alliance, and this covers most of my PvP requirements (seriously, thats all I get, EVERYONE wants them dead!) I have tried as a Junker indie and found some RP interactions, but not alot. Most just ignore me, unless I try to smuggle, but this can prove costly for me (I getr halted a bit in my Slave Liner, but it is fun!)
Plus with my limited game time any faction with a rigid structure to adhere to would not work, as I would be forever stuck in the lower ranks. I have also been a pirate to, but unfortunately for me I bring my morals into the game with me, and I just feel bad about stealing:$
Any factions with a good cause to fight for generally works for me though! (eg Xenos) anyone else like that in the same vein? Gaians? What are they like for fun?