It depends on what you want to do with it.

Drum & bass, Trance, Techno, Ambient, e.t.c get one of the Korgs

Orchestral and natural sounding instruments (piano, bass, organs, violins, and stuff) get on of the xp's. If you play pop and rock go with the xp's

I have an xp and love, there are very little things this baby is not capable of. At the end of the day Money talks as well (Refering to the XV's and the Ttiton now). Is sampling an issue for you?