which lens? sharper or greater aperture?

[mislav]

I have oportunity to buy cheaply two lenses but dont know which is better? One is Pentax-M 28mm F3.5 for which i know is very sharp even on 3.5F. Second one is Pentax M 28mm f2.8smc, and also vivitar 28mm f2.8 which both have bigger aperture, but are less sharp... help... or you have any other suggestion??? (vintage cheap lenses)

[dannybgoode]

I’d take sharp over aperture any day assuming you were using a guided setup and just expose that little bit longer. 

Even unguided I’d take a sharp f3.5 over a soft f2.8 - you may well find you’d end up stopping down to compensate for the softness anyway.