No question. Emu Sp1200, really.
If you need thick beats (especially BD's).
Depends on what you're up to.
If you need this groovy electro-feel, than I'd recommend a
TR-909, still one of the best beatspitters around.
The MPC's are very good too, maybe more phat soundwise than the 909, but they lack the groovy feel.
They don't have this much of an own sound, they 'just' sound good, whereas the SP1200 gives you about one and the same BD out everytime you put one in. Sounds silly, but if you listen to Funky Shit, Smack My Bitch Up and all those overproduced Prodigy-smashers - that's the SP1200.
They come out extremely thick and the nice thing about it is, that you mostly don't need to eq them much (and don't even think about dynamic editings, that would just ruin the phatness...).
Refered to as 'the' HipHop drummachine.
They're expensive as hell, though. I saw one on eBay a few days ago, went for 2300