Single post in Your Guide to 90%+ Breeding Pairs

In my experience (whether it's true or not) the final forms seem to be higher levels which also means better egg production. I (and I'm only guessing) think this has to do with the fact that lower level pokemon don't breed as well and the higher evolutions are higher levels which means better egg production. However, the same could be true for a higher level first form of a pokemon as well. I don't know 100%. TL;DR -- use higher level pokemon, preferably the final evolutions, because placebo effect says that they breed better.