Personally I'm a big fan of Zeiss Tessars, having owned 4 examples (current one bought just a couple of weeks ago). These give a contrasty and therefore sharp-looking image even at full aperture in the center, it takes quite a bit of stopping down for the corner sharpness to become respectable and it never quite matches the center (although I only really noticed this when I made some 24" square prints). Never owned any other Rolleiflex, did have a 2.8C with a Planar to use in one studio, found it had a flatter field, higher resolution but less contrast (another contributor says he likes the contrast of his, the example I was using was not in pristine condition, but I also found the Zeiss lenses of a Hasselblad 500C I used were less contrasty than the Tessars).
I consider a Schneider Xenar to be as good as a Tessar, I've got quite a few LF examples. The thing to watch out for is the way German camera makers worked in the 50s and 60s: First they would at great expense design a great camera (like a Rolleiflex or Leica M3), then they would find this was too expensive, so they would spend even more more cutting a couple of features to make a cheaper version. In the case of the Rolleicord, this meant an uncoupled film wind (not too much of a problem) but also a diabolical shutter release - I ignore the shutter release on my Rolleicord and use a short cable release even for hand-held work. The upside is that Rolleicords, while being capable of excellent work, seem to be very unfashionable at the moment and and cheap to buy.