I really like the werksan economy training bumpers (
http://www.catalystathletics.com/sto...u cts_id=161).
We have used these since we opened here (4 years now) and out of 7 full sets and several additional pairs of 10s and 15s, we've had problems with only 2 10s cracking a bit, and I believe that to be from some of our less attentive lifters (and likely lifting class people more) loading a bar up with too much change and only 10 kg bumpers and/or dropping their bars crooked.
That said, I wish the old Mavriks were still available because those were my all time favorite bumper and seemed to be nuclear holocaust-proof.