If you're not in-the-know, the Akai APC-20 is, by far, one of the dopest MIDI controllers ever made (so far). Besides the fact that it's automapped for Ableton Live, you can switch the pads into Note Mode and chromatically play your sampler, instrument, or drum pads. Needless to say, it works extremely well with Ableton's Drum Rack. For this reason alone, I decided on the APC-20 over the APC-40 since the latter curiously doesn't have this feature, although it's apparently doable via a soft-hack.
More so than anything, the APC-20 is a replacement for my M-Audio Trigger Finger, which I absolutely loved, however I quickly outgrew the four faders, and I was only using it for triggering scenes and samples in Live, and not so much for typical drum pads.
I've only had it for a few days now, and I can say that it's truly one of the best pieces of kit that I've ever purchased!