don't know acid, thou :?
but ableton is probably one of the most stable softwares out there...
i have never ever heard of any crash whatsoever from a user!!
and pretty much a very fast becoming standard for loop sample based LIVE use (it's merely developed for live laptop performances!) and production, takes VSTs and AUs!!!
is dead easy to use and you can manipulate nearly everything on the fly!!!
definetely worth a closer look, i know lots of logic heads (because they work a lot with midi) who are using ableton more and more for production...
Ableton Live is a much better investment in my opinion than Acid Pro 4.0, I used to use Acid Pro 4.0 and I did enjoy using it but Ableton is the king. Check out Ableton Live v5. Some of the benefits are that it's very flexible, once you get used to the interface and how the basic functions work you have unlimited options to route your audio, midi support is getting better and you can use it live or in preproduction it's equally powerful plus much more!
Years ago, I had Acid 2.0, then started working with Live 2... Then 3... Then 4... As soon as I discovered Live, I never went back to Acid. Though, Sony has since bought them from Sonic Factory and made many changes of Acid, I was so pleased with Live that I never looked back. Now Ableton has just completed the beta testing of Live 5!!!