I haven't used Peak since the OS9 days, I still do have it on a partition (WHY???)
Anyway, its been buggy, but cannot be sure since I haven't used it since OSX. One thing is that Peak has the PowR algo ,and Quattro uses another algo- a shaped gausssian noise for dither. If that matters to you.
IMO Quattro may have less bells and whistles, but does the job, and the price is great.
Download the demos, after all its about how you feel working with it, and what you can accomplish.
T