It would be an interesting statistical analysis to figure out if it's better to play a bunch of strong opponents, a bunch of weak opponents or a mix.
I've always thought that one of the most important qualities in an opponent is a team that forces you to speed up. If you play an opponent that shows you a different style, you can scheme around it, often with little preparation. Of the opponent is passive, sags back around it's own net, and blocks shots, there are different tactics you can try. Reverse the puck, move it low to high, get shots to the net and crash for rebounds, etc. As long as the opponent is passive and you have 60 minutes, you can eventually find a way to have success, even if it is an unfamiliar defense.
However, if the opponent is more aggressive at taking away time and space and forechecks harder than you've seen before, it takes a while to adjust. The puck movement and decisions have to happen faster. If you're accustomed to playing with the speed dial at 7 or 8, it's a big difference to try to play at a 9 or 10. Everything becomes harder: passing, shooting, even skating with the puck. Colgate was a fast team, but UMD had seen speed before, and recently. When Ohio State came at BC hard in the second period, it had been a long time since the Eagles had been forced to play at that tempo.
IMO, you improve most when you play opponents who force you to get better, because your usual level is no longer sufficient.