I've always found this hard.
To get an acapella or any solo instument to fit into a track perfectly is where alot of my productions are falling short.
I Find SX is pretty decent & a little easyer using the hitpoints to get the right timeing. Wavelabs is good quality & also the prosoniq time stretching plugins. Another plugin to look out for is phatmatic but i tend to miss use this plugin to get interesting FX.