Vegas also does a great job with looping - just set a region, set to loop and record. It will go back to the beginning of the region and keep recording. I believe you have the option of having each take on the same track or a new track (or is that Sonar?). It's been so long since I've done either, I forget. But I remember LOVING ADR work in Vegas.
I had a singer lip-synching for a short music video using Vegas for everything. I set up a monitor and headphones so that he could see and hear himself in the original exterior taping, then made a loop region and let him sing the piece until he was happy with the results. Each loop made a new take on the audio track, but since we only used the last take, the rest was easy.