If you plan on keeping it simple with the '030, a Spectrum 24/28 is a nice little card. Passthrough for Amber, Z3, snappy performance, and clean picture quality. Piccolo SD64 would be a better performer, but they are somewhat rare. I'd steer clear of the Cybervision 64/3D, no passthrough, so you'd need two monitors or some other extra BS.
Picasso IV is hands down the best one, but it's expensive, and overkill for an '030 IMHO. It has its own scandoubler, but it can't be easily calibrated for perfect game scrolling. Some argue that the Cybervision 64 (non-3D) is best suited - performance just a bit below the Picasso IV, and it has a passthrough for Amber. That's what I run in mine.