As a new member of this site, I don't know most of you well enough to chime in with names you're guarenteed to know. I will say that as far as deadly players go, HolySwords4Him has a reputation that preceeds him. A friend I play with who isn't a member here has spoken at great length about getting his @$$ kicked by HolySwords and crew. Now, not to sound overly arrogant, but having faced off against him once, I felt I was at least able to hold my own (even if I lost), which is encouraging.
Back on topic, most of you may not know these guys, but the two deadliest players I play with on a regular basis are ImALazyCanadian and JACCX023 (who just signed up here a few days ago). Friendlies are Genie of Funk and Separate Titan, who also just signed up.
As for established members of this community who I think are among the nicest, I'm going with BrotherSgtMongo (who invited me here in the first place), Darksaint, and I...... O... (can't remember his whole name right now, current leader of the Black Templars).