Plastikote T-235 is great stuff and will stand up to any auto paint I've thrown at it. However, it has to be sanded. (It wet-sands magnificently with #800 Wetordry, used wet.)
I still have a few cans I save for "special" jobs. My standard primer these days is the cheap Walmart stuff. Light gray, goes on thin, dries smooth and fast, and stands up to ALMOST anything. Almost cheaper than Walmart Cola, too. What's not to like? It's one of the few genuine BARGAINS still available in Model Car World.