Depends on your format preference. Bang for the buck? Probably the ETRS(i) in 645. The SQ series(6x6) can get pricey, especially if you're not buying a kit(body+WLF+120 back+80/2.8). Things like 120 backs and WLFs for the SQ series can be expensive. The GS-1 is a very light, portable 6x7 camera. They're a bit rare and usually a bit spendy for backs, lenses, finders--if you can find 'em. Lenses are very good for all the modern Bronicas. Nostalgia aside, I'd not bother with the ancient, mechanical S series or EC-TL--too many parts, service, and age-related issues.