I'm rather new myself, but I have to say: this forum has a wealth of information. If you've got some cash, I can say without a doubt that the best frame out there is probably a worksman. Schwinn cruisers are very good too, and easier to find used, yet with a good chance of still being very workable. My Micargi hasn't given me any trouble yet (but then, I greased the crap out of every moving part on it, and tightened every bolt whilst occassionally using locknuts). Many will say use a steel frame. If you want to try an aluminum frame, I would ask around on the forum first to see if anybody had trouble with it.
Best engine, by common concensus, seems to be the Grubee Skyhawk or Starfire. I hear a few good things about Raw now and then too, and Jet. And the vendors that advertise to the left and right here tend to be spoken of rather highly. Most of them, I believe, are also members here. You buy from them, you got problems, you go here and write, they write to you. Nice arrangement.