Changing Tempo, both midi and audio, where to begin

This is a new adventure for me. I have a live multitrack recording. I have sucessfully converted the drums and bass to midi using audio snap to create a tempo map, Drum Tracker to capture the drum hits.  The tempo does wander a bit. I would like to even the tempo, but keep two of the audio guitar tracks, and some harmony vocals.
 
So, is it best to split the transients to clips, straightline the tempo and quantise, or utilize groove clipping in some way?
 
Or something altogether different?