I don’t know that they are, or that there is, a “best” way to do them. I would think they would be helpful with both hardness and stamina, but I don’t think that doing them with or without resistance would add to size, outside of maybe a little additional hardness. The only caveat I would attach is that you shouldn’t do a bunch of either too close to when you have sex It’s been my experience that if my BC muscle is fatigued I cum quicker. So give that muscle 24 hours of rest before any big dates I guess is what I’m trying to say.