Sorry about the lengthy post, got a bit carried away...
D&D 4E is a great system imo, though in my groups they haven't been so much roleplaying games as dice rolling games with the odd in-character remark. My groups have always been filled with powergamers who cared more about optimizing their characters (usually by copying optimized builds on the Internet) than roleplaying though, so if your friends aren't like that it could work out better. When DMing it got really hard to balance encounters for them as some started out ridiculously powerful - a rogue which only misses 5% of the time and regularly one-shots level 3 mobs on level 1 - while others were more "normal". If your group can agree on playing it more in one way than the other or agree on some banned stuff it shouldn't be a problem though.
I prefer Vampire: The Masquerade myself. It's more roleplaying than dice rolling, and as a DM I asked each player to flesh out their character extensively before starting (even going so far as saying I needed to approve of them). I linked them to this, [http://bakersfieldrpg.com/Documents/Vampire%20the%20Masquerade%20-%20Character%20Creation%20100%20Questions.pdf] telling them that they shouldn't answer every question, but that they should at least have a look and see if they'd missed something. We ended up with a very diverse group and all of us were really engaged, hardly ever speaking out of character.
I found that Vampire required a lot more effort from the leader by needing a more complex story, though again that may just have been due to the groups I played with. It was hugely more rewarding to see the players debating between themselves how to proceed, what it could all mean, if they dared go head-to-head with a Sabbat pack so early in the game etc. than to just see them move their characters around on a map, role some dice and tell me the result. It all depends on how the group wants to play of course but I would've loved to finish my Vampire campaign. Alas, I had to move away from my group
Edit: If you go D&D 3.5, I recommend some house rules either on particular combos (difficult if you're new to the system) or restricting yourself by tiers as described here. [http://brilliantgameologists.com/boards/index.php?PHPSESSID=bc18425e5fa73d30e4a9a54889edf44e&topic=1002.0] Having an optimized wizard in your party makes the rest of the group unnecessary. I know this from experience and it's not a lot of fun.