if you want to block IGF and estrogen - go with the nolva - like if you are on deca or fina - if you want to block the est, then go with arimidex - although I think it doesn't as much block it as it does prevent it from aromitising (sp?) or at least most of it 98% or so.
proviron, IMO, is used more if you want to reduce bloat, and if you want to get nice hard erections.