Lots threads on this one. It's a tossup between clomid or nolva. To cover all your bases go with both. Clomid apparently brings your boys back faster. Well then there is torem which is increasing in popularity. There is no definite answer. People are all over the map on this question.
Personally, I think clomid and nolva are too similar in nature to _really_ make a difference and Nolva has been the staple serm since the beginning of time. I went with Nolva but I'm day 8 on mdrol and not in pct so we'll see I guess.
My balls are still mammoth and the body is great at returning to homeostasis with little help imo so I'm not that worried.
So saying all that, if you want to be reeaaalllyy careful and don't have a budget, get both otherwise flip a three sided coin.