Which level 4 monster is the best?

Of course, Vampire Lords are stronger, but that's an overstatement!
In my opinion, only golems have a chance, albeit a small one, but they still have a chance!

Listen, I already understand that you have a personal fondness for Golden Golems, but the fact remains that they have absolutely no chance, and I have no idea how you even tested that. IMO, not IMO, but in this example, i.e., in the confrontation of 4th-level units, no creature can oppose the Vampire Lords, not even the slightest chance. I don't favor Vampire Lords (my preference is for Ogres), but they are rightfully the strongest among their levels.