I was using the SOLO program that came with SD2....at first. I was having a glitch with it not recognizing my MIDI connection. Tom Roady showed me how to load up SD2 in GarageBand and it worked like a charm, the only problem with GarageBand is that the only thing I could control with my MIDI foot controller was the volume, and in SOLO the program would crash if I used the volume pedal, so basically, I had a $400 paper weight that I didn't think that I would use again. With GarageBand, I could load multiple kits into different tracks, but the only way I could switch between kits is to either use the mouse pad, or arrow up and down to select the kit. Then I went down to Atlanta for the Z4 upgrade and Dr. Shark introduced me to Ableton Live and showed me that I could control almost every function in Ableton with my FC-300. I was blown away, the light bulb came on and the heavens opened up. Ableton is the same as GarageBand, giving me the ability to load multiple drum kits into different tracks, then I can assign a track to a foot pedal on my FC-300, and it is instantaneous, the kit changes right when I push that pedal, no delay.
So, I guess to answer the question regarding Ableton or GarageBand, or any other comparable program, it would depend on what you are planning on doing with it. GarageBand is easy to use, not much of a learning curve, but has limitations. I used it to record some tracks to include piano, bass, and horns and it sounded great. I was using GB to play out live as well, but I was only using the one kit, and could not use my FC-300 the way I had originally intended. With Ableton Live, there is a bigger learning curve, it has all of the same functions that GB has but allows you to use a MIDI controller to control the different functions in Ableton. You just have to figure out what you are trying to do and find the right program that will give you the functions you need.
Hope this helps,