For just a single RP session, I'd go with one of the roleplays I've had with my friends in past years for FHORD, actually. None of us usually did FH RPs outside of FHORD, so those would usually be pretty memorable (and would often derail from serious emotional RP to jokes, which is also totally acceptable).
As for an ongoing RP, I've been in an RP with someone on another website that's been going on for about 3 years. We've created an entire land and universe around this RP, there's so many characters and we're always trying to build on it some more.