I have read that usually TLR lenses are very sharp.
But I have not found good reviews on Yashica model.
You get what you pay for. Of course the more expensive Rollei models will be sharper. The Yashicas are pretty sharp but are in the $100-$200 ranges. Also, something to consider is that the Rolleis will probably be better maintained as people tend to baby them more and get them services more regularly.