I have an M42 Pentacon 29/2.8, Pentax K SMC Takumar 100/4 macro, and OM Vivitar 19/3.8. They are all towards the cheaper end and the 29/2.8 and 19/3.8 are a bit soft in the corners wide open but still a lot better than the 18-55 kit lens I got with my 20D. Stopped down past f5.6 they are pretty sharp and since I use them for landscapes mainly this is no problem. The other great thing about older MF lenses is that the build quality on them is a lot better in many ways than modern cheap lenses. Mine are all metal and even after 30 years they are in excellent working order. Because they are primes they are often much smaller than modern zooms.
In aperture priority mode they are pretty handy as my adaptors have AF confirm so there is just focusing to take care of, and handheld I wouldn't be using them stopped down much anyway.
The 100/4 macro lens is fantastic though, really sharp even wide open and way better than anything else I could have got for £75. I would definately recommend an adaptor with AF confirm, for the extra £10 or so its well worth it.