((Easy....Virtue....and I've tried them all))
Virture has the rep...you might find the reality to be rather different.
"And in this moment, I will not run.
It is my place to stand.
We few shall carry hope
Within our bloodied hands."
Virtue has been the unofficial RP server since beta. Doesn't mean there's RP all over the plca, but the chance of running into RPers is generally higher.
There's an established and still growing group on Pinnacle called the RP Congress, which is a collection of different themed SGs and solo heroes. We accept all RPers whether you're experienced at roleplay or not, the people there are good-natured and up for showing new people the ropes.
Check us out at www.rpcongress.com
I'd say virtue, when I got my CoH game, I asked around and got the same answer everytime. I do find trickles here and there, but i'm waiting to find the BIG groups you know? Maybe I'm just hanging out in the areas where non-RP-ers hang? 0.o
A good way to know for sure is to read other heroes info, the stories and background info you read can be pretty interesting
Virtue
Galaxy City is the main roleplaying zone.
Head over to Gemini Park, there's very often people hanging around chatting in character.
Good question, great answer!
I'm heading over to Virtue myself. I've been on Champion and Victory for 2 weeks and haven't found anybody to RP with. I have been rejected for having a weak build though 
CoH
Cathodian (50 Rad/Rad)
Archanix (50 Ill/FF)
Dr. Deadface (Current: 40 Rad/MM)
RP'ers are rare on Victory, but there's a few dozen of us now always looking for more folks. If you're interested, send me a tell, @Spackle in game, and I'll hook you up with our global channel VictoryRP. We have an open RP Day every Sunday in Gemini Park, 12PST/3EST/8GMT.
Still, Virtue's the place with the most RP'ers by far. I hang there about half the time, too ; )
Was wondering Which is probably the most Role Playing Server?