I've owned both previously. Here are my thoughts (YMMV):
I actually traded in my XP-30 for the Triton (classic) because I was "wowed" by the Triton after playing it. In hind sight, probably not the best thing I've done with a gear purchase.
The XP-30 was loaded with great sounds - bread and butter stuff as well as having the orchestral card built-in (I use a couple of these patches on a orchestral card loaded in
my XV-3080). Also contained the session card which IMO, has a better piano than the Triton. This is subjective, but I could not find one stock piano on the Triton that I liked. I don't recall exactly, but it seems there was a patch somewhere in the XP-30 called "B3 Filth" or something like that. Really good organ sound I used live. You could always expand the XP-30 with the Keys of the 60's and 70's card (which I use in the XV-3080). Pretty cool organs and other stuff from that era, and really expressive for live playing. I've recorded some of the patches recently form that card as well. Got card off eBay for about $130.
Triton has some cool organs as well as electric pianos (some of which were rich and thick), but to me, it seemed more of a "hit one key and be amazed" synth. I remember using the Triton for stuff like the main synth in Abracadabra, Separate Ways and the little "synth hits" in Footloose.
If you're looking for more of an all-arounder, I'd choose the XP-30.