of course the look of the lenses is important, but i feel that o lot of what is called the "the look" can now be created in C1, so i like to get the cleanest, freshest, most balanced starting point (file) to add and take away later...good contrast and clean color is very important to me....it is nice to not have to sharpen in software...in the end it all comes down to how oyu work and how you get your point across...i will give my personal experience and opinion...
i went from a P20 on rollei to a P30 on mamiya...i looked long and hard at the contax as well but decided for the mamiya for a couple of reasons: i like the lens range better, better options for me, all tests i read placed the mamiya over the contax lenses, mamiya is a considerably cheaper system...both have the *%$#@** 1/125 sync speed, the contax has faster lenses (which i never utilize), contax has the grip (only real advantage in my opinion)...i also already had a 645AF body (which i sold to get the AFDII anyway)....both can accept all kinds of lenses with adapters (as far as i know)
about the lenses (other then the tests, my personal opinion): mamiya lenses are great...the 645 lenses are very good to great, all RZ lenses i have owned are great......almost all zeiss lenses i owned with hasselblad were disapointing especially for the price(funny to me that the 120macro keeps coming up...maybe i had a lemon, my canon macro was far superior, the zeiss was unusable f16-f32 on DMF backs)...i had the same situation with zeiss lenses on the rollei...but there one has the option to shoot schneider lenses.....ahhhhh they are the best, there is no comparison and with the rollei one can compare between zeiss and schneider lenses on the same system...not even close.....i guess for the last 50 year everybody always said the zeiss lenses are the best and at one point it just stuck....they are of course good lenses, but compared to others (and again especially for the money) the seem to be behind....maybe they stopped actually putting money into development about 15 years ago?
fuji's lenses on the 680 and 690 series are in the same league as the schneider lenses for the rollei, everything else is a step below (and some zeiss glass even below that)...the mamiya 645 lenses beat every price/value comparison, the most expensive ones on ebay are the 35mm and the 120...the 35mm is a bit of a let-down, but again i bought mine for 800....for a 35MF lens! yes it has CR when shooting into the light...which WA lens does not?
for me the mamiya is a phantastic system, cheap, handles great, great lenses....i am superhappy, but i am waiting for the Hy6 to come out..the schneider lenses are simply the best.....