Evercoat Quantum 1. It's a hybrid polyester/epoxy filler. Sands great, and will go direct to metal with no worries. Everyone will likely advise against it, but I've had it on several vehicles for 5-6 years now with absolutely no problems.
Matt 69 Dart Swinger 340 83 W350, Megasquirted with 46RH Old news: 72 Demon street/race mobile Latest: 70 Duster backhalf car and even more