definetly go with the Bosch O2 sensor. Bosch has pretty good quality and the generic bosch is like $80 while the OEM is like $200. (bosch makes a direct replacement but it is also $200, as far as i know the only difference is that the direct replacement has the OEM plug wired to it With the generic you have to do some crimping.)

A good rule of thumb is to think what happens if that part breaks i.e.:

PCV valve breaks, you buy a new one, no biggie. go aftermarket.
Timing belt breaks, chances are your engine is shot. Go OEM