In Germany, that is somewhat hard to decide - Bronica were reasonably well distributed here as well, so they aren't quite as rare and expensive as in some other countries (Mamiya were pretty much globally represented, while there are many white patches on the Bronica map).
In general, most of the M645 series (except for the 645super, which was a stinker) held up better than the ETRS - the non-interchangeable back ones in particular are hard to kill. And M645 and their lenses are more widespread, often younger and cheaper. But a good ETRS(i) is a excellent camera, and with its leaf shutters better suited to flash use.
Stay away from the M645super. And both with the ETRS(i) and M645pro(TL) carefully test the magazine linkages, and with the ETRS(i), also check the lens (shutter) linkage - wear and loss of reliability of the linkages are the most common issues with either camera. Beyond that, and with the plain old M645, the usual rules for buying a small format SLR apply...