The bronica has now been discontinued so there are some good deals out there. Service maybe a problem in the future but who knows about the future. FWIW, both systems are comparable in lenses but ergonomics differ significantly, for me anyways. I have always appreciated the nice speedgrips of the bronica and coupled with the AE prism, it makes for a nice quick shooter. I know the mamiya also has a motor option that makes things handle faster but they are heavier and a tuch more awkward to handle.
As for durability, according to my service guy, the bronica seem to have more problems but he tempered that comment with that the cameras that he sees are from working wedding photogs who were not nice to their equipment. Beatup and lots of rolls of film through them.
Bottom line, go play with them and see what handles better for what you want to do. You can get volumes of messages on arguing what is better but its your money, so go borrow as much as you can so you can go play before plonking down cold hard cash