I can tell you what I've found from my short experience so far. I started with an old Roland W-30. It is a performance instrument, so I can use the keys to trigger, but there are really no other useful controls (sliders, dials, etc). Now I'm looking at getting another controller with more functionality. Two that look good are the Alesis V25 25-Key, and the Arturia KeyLab Essential 49. The other thing I've found very useful is to have some virtual midi software to go along with the midi hardware. Both of the examples come with midi software apps.