It's Virtue.
*Covers up Virtue character names*
Seriously.
I vote for Virtue as well...
Like any other server, roleplay can be difficult to find initially, but as soon as you get into a circle of roleplayers or a roleplay SG, things quickly get pretty intense 
There's even some roleplay in Poket D, squeezed between all the leet talk and WoW players -_-
Don't try freedom, though...
buncha ungrateful d00ds...
There's also some roleplay to be had on Champion server with two recently merged coalitions united. It's more supergroup-focused than I think Virtue typically is, but still a good time to be had.
The Alliance of Champions side of things can be accessed through links in my signature. The Crusaders of Champions forums can be found at http://www.crusadersofchampion.com
There is also the Champions United on Champion, at www.championsunited.com.
Is there a general concensus as to the most RP-intensive server? I've heard Virtue, but I wanted some confirmation before I get too heavily into a new toon.