Lead with some kind of coating that's supposed to prevent lead build-up in the barrel. I've tried BBI (9mm) and Precision (.45acp). I haven't shot enough of either to have much opinion on them...but the test batches of 200gr .45acp I loaded were very accurate.
Someone's bound to chime in that plated is the best of both worlds (cheaper than FMJ, cleaner than moly). The only tumbling I've seen with my own reloads has been with plated bullets, and the same load that shoots fine from my G17 tumbles from my G34. I'll pay a little more and stick with jacketed bullets that work in all my guns.