Masp, Bambi is right. Whatever you buy, you will most likely be happy with. They all perform the same functions, its just extraneous bits of detail after that honestly.

As far as older Olympus and Pentax lenses. I know Pentax has a huge range of fully manual lenses and auto lenses. The older manual lenses tend to be quite good and extremely sharp if you are willing to adjust the focus and aperture manually.

Olympus lenses are the same way from what I understand. I have very limited experience with them, but they are quite good.