Don't know about the live or x but I got an MPC rennaisance about 2 or 3 years ago and tbh wish i'd got a maschine instead - for what I do anyway. It might be great in a live scenario but for my workflow in the studio it sucks - big time. The software is utter shite (regularly crashes my DAW, forced to use the Akai VST interface which is shit imo), you can't use it as a midi controller for anything else - they're the main drawbacks for me. It sounds amazing, like everything seems to sound fat as fuck out if it, but I'm seriusly considering selling it and getting a maschine instead.
Akai software is the biggest problem imo, it always has been terrible going all the way back to the early software for the S3000 samplers, I kind of figured they would have sorted that out by now when I bought the ren, but no - it's still inexcusably buggy shit.