tebop, I've never use Logic, so I can't make a recommendation.  I read in a couple of places that melodyne was the best hands down for pitch and formant shifting, after trying it I was quite impressed.  It made the cheap plugin and shareware formant shifters not even worth the download.  I can't say if it's the best, but its very good.

You may want to ask this question on a pro audio board.  There will be guys out there that have used every pro audio editor and can give you comparisons.