PPG is the way to go. Yes, more expensive. But worth it in the long run. As far as a single stage or a base clear set up, I prefer single stage, especially for solid colors. Reason being its just so much easier to deal with repairs down the road, if you get a scratch you can just touch it up and color sand it flat. Definitely not as easy to do that with clear coat, especially if you have to do anything beyond a small scratch (like repainting a partial panel).
Now, I did say solid colors. If you go with a metallic paint (like B5), you really can't do those kinds of repairs anyway. They'll show up even after the repair because of the metal flake in the paint (nearly impossible to match), so going with a clear might be a better bet since the clears tend to have a harder finish than the single stage paints, and you already can't do any kind of spot repair without repainting an entire panel.
