I don´t know why, but most of the Yashicas I´ve seen had the poorest VFs before being properly cleaned of dirt and haze. Of course a proper cleaning does miracles and they recover their original transparency.
From the high side (pricewise) I second Brian´s opinion, the M3 is perhaps the best I´ve ever seen, and besides it has a mag of 0.91 which makes it more attractive. For Us (who get older and need glasses to read decently), good contrast between VF and RF patch as well as a VF closer to a 1:1 ratio, IMO is the best.
In the low side, the "old" Canonet QL19 and the Mamiya Super Deluxe have very good VFs (for my taste), it is good contrast (not as good as the M3), but far better than others. Unfortunately they have fixed lens.
Many 35 mm and MF film cameras, some weird cameras... and nothing digital yet!