the standard would probably be a Traktor Kontrol S4 because of its tight integration between hardware and the Traktor Pro software. both were made by native instruments, after all. there's a 1 to 1 correspondence between what's on the screen and what's on the controller.
the great thing with controllerism is that traktor is completely mappable. all you really need is a decent amount of buttons & knobs and some imagination. for example take a look at dj storm eagle's custom mapping for the numark total control. it's a fairly limited piece of hardware but with a little creativity he's able to get a lot more out of it. (
http://www.djstormeagle.com/midi-mapping.html, checkout the youtube video).
check out all the djtechtools articles and videos, ean really pushes the limit with what's possible. read a lot, practice a lot, and try new ideas. there's no limit with controllerism.