it depends. If I'm bulking I will run a low dose of nolva just for gyno purposes. I don't really care about bloat, and some estrogen is productive while bulking. Which is the reason I wouldn't use an AI, just a SERM while bulking.

As for an AI I've only used Ldex. I'm curious about letro, but even more so about aromasin.

Generally it's a SERM while bulking, and AI's while cutting.