The market is crammed with MIDI/USB controllers at any price and picking the right one for you seems like a difficult task. First of all, consider this: there is no such thing as a controller that's perfect for everything. When you play a sampled piano, you definitely want a hammer-action 88-key controller. When you play a synth solo, you need great aftertouch, which a fully-weighted keyboard would make very cumbersome to engage. When you play a virtual Hammond, you want a keyboard that feels like that of a Hammond, which means lighter/looser keys. Yeah, you guessed it, I do use three separate controllers, depending on what I'm playing. The Akai MPK series falls in the second category.
The Akai MPK 49 and 61 (except for the number of keys, they're identical) have carved quite a reputation for their build quality, which is the first thing that you will notice about them. They really are built like a tank. Everything feels solid and rugged. I wish I could see this kind of build quality in many other products. Besides the keyboard, these controllers include pitch bend and modulation wheels (both covered in thick rubber, which gives them great grip and makes them feel really solid), 12 pads (with 4 banks, for a total of 48 triggerable MIDI notes), an arpeggiator with several patterns and a latch button, a transport section, 8 faders and 8 encoders (each with three banks, for a total of 24 items controllable from faders and 24 from encoders.)
The MPK 49/61 keyboard falls in the "love-it-or-hate-it" category. It's definitely stiffer (as in offering more resistance to your fingers) than that of competing products, a fact that Akai acknowledges by calling it "semi-weighted." Personally, I love it, and I suspect that any trained pianist would enjoy it just as well. Stiffer means more responsive, and this keyboard is incredibly responsive. Yes, if I need to play a virtual Hammond, I'd want something looser, and that's why I have a third controller besides the MPK and a fully-weighted 88-key controller (it could be something cheap, remember that you won't need any aftertouch for that.) But it's only for that, and therefore rarely used. The aftertouch on the MPK is incredibly precise and easy to control, something that few controllers can boast.
The drum pads are stiff too, and that, unfortunately, is far from ideal. You need to really bang on them hard to trigger high MIDI velocities (>100), while lightly tapping may not trigger anything at all. True that pad sensitivity can be dialed up from the menu, and that seems to help somewhat. Also, there's a button for full-level only, although, of course, that kills dynamics. The truth, however, is that the pad response is very disappointing. Fortunately, the fix is pretty easy. If you go on YouTube and search for "MPK pads", you will find dozens of videos that teach you how to make the MPK pads just as good as those of the MPC series. I suggest you spend a little money ($10-15 or so) to get one of the good retrofit kits on the market rather than go for a more "redneck repair" solution like using duct tape, whose adhesive can actually seep into and damage the controller's electronics.
This is what I used and it works great: MPK pad upgrade
This video shows you how to install it in 15 minutes or so: MPK49 pad upgrade kit review - YouTube
The MPK comes with 30 presets, 13 of which "generic." All of them are fully editable. They include Live, Reason, Cubase and Sonar among DAW's, and then one for Arturia synths, Rob Papen, Arkaos VJ etc. If you use any DAW other than those four, however, you will have to configure the controls manually. Or maybe someone has a script for you available for download (Google is your friend...) My MPK worked fine with Cubase 6 right off the bat, except for the transport section and the arpeggiator. Since I never use the onboard arpeggiator and I have other controllers that handle transport, I haven't bothered looking for scripts on the net, but I know that they are out there. Once again, google the solution.
The MPK 49 and 61 are not cheap ($399 and $499 respectively), but you can save $50 or more shopping on EBay or online discount outlets. These prices, however, align with those of competing premium controllers manufactured by other brands. If you like a stiffer but more responsive keyboard, this is definitely the one for you. If you are a beginner or your main instrument isn't keyboards, you might be better off with a controller that has less "inflexible" and more "forgiving" keys.