The akai synth is more polite sounding, the microsynth sounds like the devils bowel movements and the MuRF is quite different. It is more a percussive effect/stereo phaser/whooshing crazyness/i don't know what.
I love my microsynth and bass murf. Both are fantastic, top notch pedals. Check moogmusic.com for murf samples, and ehx.com for microsynth demos if you need more info. I'd check the normal murf aswell as bass murf samples, too.
As for the compressors, I'd go for the black finger as it is not that much more - and it is said to be one of the best compressors around. The black finger may be large, but the white isnt any better, being Qtron sized.