That's a difficult one...
Fortunately i have both Roland XP-50 and the KORG Triton. (bought it 2 days ago)
I've got the XP for about a year and it's the best synth i ever heard. Especially the pianosounds and all other acoustic sounds.
Now i got this triton, and that's at the moment a whole greater category of synths. (more expensive)
And yes, the sounds, interface and sampler are great!
So i think you got to look at your budget and decide. They're both great synths.

Angelo