They're both a tie in my book. Right now it's very hard to find the Pro2 so I would personally buy the Abit. It has a bad rep on these forums and has gotten to the point now where people are really laying a bad rep for it, but if you look at Anand's review, you'll see he loved it. The only problem with the Abit is of course people say the "RMA rate is horrible", bad quality control, etc.. but I have had no problems with my BX-based BF6. Now, count me lucky, but it's been great. The MSI is basically everything you'll want, except it has all of the onboard sound crap by default as well as a CNR slot; which I doubt I would personally ever use. The MSI board, however, is cheaper and probably more stable - I would also speculate that it has less problems as far as DOA issues.
If you can find it, go with the MSI.