I'm using what could be considered the world's most expensive MIDI controller, a Yamaha Motif XF8 ($3400 + $400 for the firewire connections and expanded memory options), simply because it is unparalleled in its functionality. Not only is it competent in stand-alone mode, but it also offers the functionality that I need as a MIDI controller for orchestral music. I have paired it with an Icon Pro G2 ($600) and one of its expansions ($500) for 16 additional channels of faders and knobs and all-around fiddly bit goodness. I am, in combination with these two bits of hardware, using an Akai MPC Touch ($200) for percussion, in MIDI controller mode. The result is a gobbly gook of high-quality hardware that is quite frankly, overkill for simply using as MIDI controllers. All I can say is, when I buy hardware, I overbuy.

Really think about the kind of work you are doing and buy targetted hardware for the specific task at hand. Quality matters, especially if you mistreat your equipment from time to time.

If you are a pianist, buy a good, solidly built, weighted board with USB connections for MIDI. Yes, you can go cheap and buy older hardware with actual 5 pin MIDI ports, but, this kind of thing can present issues in signal delays. Don't go cheap. Buy what you need from the start. If you aren't a pianist, lucky you, you can save a ton of money and headache on not purchasing weighted keys. I still highly recommend buying a larger board, 76 keys at a minimum, preferably, 88 keys. There is nothing more obnoxious than having to pitch shift because your board just can't do the lowest of the lows or the highest of the highs. Finally, and this is just my personal opinion, buy a separate device for faders, buttons, pads, and knobs. Most boards, unless you are willing to spend thousands of dollars, have cheap faders, buttons, pads, and knobs.

Overall, if I had it to do over again, the only piece of hardware in my setup I might consider replacing would be the Motif XF8. Its just way to expensive for what I effectively use it for nowadays, and in all honestly, you can get a weighted 88 keyboard with a fantastic feel and good in-built piano sound for one quarter of the price, and then use other hardware to provide for the knobs, faders, buttons, and pads that are needed for other work. Otherwise, the Icon Pro G2 and its expansion, absolutely I would buy again, and the MPC Touch, well, ok, maybe I might buy a less expensive pad machine, or, one with more pads but without the screen.