How to select a good quality frame?
I think most any frame is going to suit you just fine -- consider size, riding position, cost, and weight. Outside of that, one generally doesn't have to worry about frame failures or anything of that sort, with the exception of crazy carbon racing frames.

I think this is the point where you go to a local bike shop and try a few of them out -- look at what's available, and choose one you like (that is, that you feel comfortable riding with).

As far as things like welds, you really don't have to worry about the frame failing on you. Better welds are lighter, but that's really the extent of it.