I know this is an older topic, but figured I'd throw in my druthers. I think raw copper and bronze are perfect for practice and for sale. I'd steer clear of coated or enamel coppers if you can, not to mention that raw copper is less expensive anyway. Plus, you can oxidize it and it looks phenomenal, but you can't oxidize coated metals. If you like the look of silver, the only kind of plated wire I like is at JoAnns (though I think MonsterSlayer sells it as well) and it's a sterling silver plated copper core wire. The plating holds up phenomenally well. The draw back is that it can't be balled and it can't be oxidized, but for a beginner, this is a great quality wire.
I avoid Parawire at all costs because their dye lots are inconsistent and if you get into wire weaving, the enamel comes off way too easily.
For standard wrapping (a la wire sculpture website), usually a 20 or 22 gauge is good. For wire weaving, I prefer 20 or 22 gauge for the base wire and 28 gauge for the weaving wire, but it really depends on the project.
www.jewelrylessons.com has a TON of free weaving and wrapping tutorials. You can download 2 freebies a week, so it's a good place to visit for tips.
Hope this helps.
Nicole