I think if your looking for something to use in a live DJ set, then something with pads would be great - saves taking along a keyboard and if it's one that you can use sticks with, then it'll look more spectacular.
If you want something with nicer sound, then I'd say go for an EMU for general sounds or an Akai for drum hits. I love the output boost on my EMU for just about everything - it gives real a nice characture to snares and bassy hits that nothing seems to match.
Or....Get both! I have a Roland HPD15 drum pad that I use to trigger samples off the EMU which makes a pretty cool combo. Drum pads on stage can't be beat to get people going I think.
Good luck with the choice Alex.