I use the Mackie Control with Samplitude Professional. I agree with Jeff that having a hardware transport control was near the top of my list for reasons to get one. THE best thing about the Mackie Control is that it displays track names. This is especially important if you're working on a 24 track project with just the 8 track main CS and no XT sidecars. Then you can bank switch or track scroll and not have to figure out which track you're looking at. The touch sensitive faders are awesome too, as they sense your fingertip on the fader, and know to hand over control of the fader to you and record your moves the instant you touch the fader, and to stop recording your moves the instant you take your finger off of it.
But it is a fairly large purchase, and won't do anything to actually improve your sound. You need to prioritize it relative to good monitors, mics, preamps, etc. You can find them used for around $600, maybe less. New I guess they will be somewhere in the $900's, maybe less.
There are other options of course, but for me the quality and features of the MCU was the sweet spot, with less expensive control surfaces not being worth owning, and more expensive ones not worth the extra bucks.
-RD