Pentax. If you watch KEH you'll often see older 645s for less then $200 in bargain condition including a 120 insert. All you'll have to add is a lens. Pentax sells I think two leaf lens in addition to the normal lenses. It can use TTL flash. The Bronicas I think need an expensive module. I'm not sure about the Mamiyas. You can also get an adapter for the P6 Soviet lenses so you can get some cheap lenses. Including the 30mm. You can get a similar adapter I think for the Mamiyas.
Every so often I think of getting a Bronica with leaf shutter lenses but I think about the 6x6 bodies. But it's not a big issue with for me.