I've purchased the external BT unit, an Alpine MRW-300/4 amplifier (accepting speaker-level inputs), and all the appropriate wiring, connectors, distro blocks, fuses, loom, etc., to produce professional results.

Much better than a gaudy rice-fest that is aftermarket stereos. Continental offers a decent option, as does Clarion, but they're both relatively under-featured. The Continental unit doesn't have pre-amp outs, and the Clarion has a white screen and won't match anything in the interior.

If aesthetics were pointless, I'd go aftermarket as well. It's cheaper and easier to implement, certainly.