32 and 64 bit. There's no easy way to test a beta and decide if it's too buggy or not without trying it as a default. For me, that's a no brainer, because it's easy to change back (as I did with the first x64 builds). Moreover, in their vast majority during the past couple of years, I've Opera development builds quite usable and usually better than the released version. Ironically, the alphas are often better than the betas.
Here I probably miss IE 8 due to some changes with IE 9 more then anything while 9 is still on along with Opera, Ice Weasel for Windows, Nabigator 9 believe it or not!plus SeaMonkey and FireFox and the default browser presently being the 64bit flavor of FF WaterFox.
While having a good impression of Opera as a fast, clean type browser I wouldn't ever again use it for opening files since it became too dominant over the Windows Photo Viewer and a few other things when set as default. So it has it's ups and downs at times like any other browser.
One of the reasons for advising to stay with one already final is that the install, uninstall, and subsequent reinstall is resulting in creating more problems rather then seeing one solved. Plus going from Alpha to beta to near release to final is always a "subject to change" factor which isn't good for something you want to see last.
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