I always liked Van Damme, he seemed to at least try to act in his movies (from distant memory Legionnaire was actually pretty good). Seagal just fluked it with Under Siege (which was good - largely thanks having a battleship in it and Gary Busey / Tommy Lee Jones) and they honed his character to accommodate his extremely limited abilities.I was 13 when it came out and was not impressed. Van Damme never really cut it for me. I'll always wish that he and Segal had a showdown back in their prime.
If you want your brain curdled, give the latest Dollop podcast on Seagal a go. It's awesomely f***ed up.