To tell you the truth, I know that these are both expensive piece of equipment, but they are both really good. I'm not sure how powerful the sampler is on the Triton, but I would guess that it's pretty good to work with until you can get something like an MPC. The sampling capabilities on the MP are hot. The only thing I don't like is the lack of time-slice, but I only worked with MPC 2000, not the XL, so I don't know what it has. Anyway, I would say if you play keys, get the Triton and save for the MP, but if your just looking for a sampler, get the MP. Ultimately I gotta tell you to go to the store and just play around with both until you can figure it out.
peace,
da muzicman