"Constantly"? Five dudes over 40 years isn't "constantly", especially since three of them were responsible for 85% of the films. Contrast that with four Batmans - including Christian Bale - over five movies!
I'd take the last two Batman flicks over the last two Superman flicks in a heartbeat. Batman Forever actually has some good moments, and B&R may be mostly a debacle, but it's at least as good as the nightmares that are the last two Superman movies...