Hi. Welcome to the forums.
From what I've heard, the Century Wavemaster II is designed for cardio kickboxing and the like. It's not meant for the heavy punishment of a real martial artist. As you can read on their website, the Century Wavemaster II has capacity for 100lbs less than the regular Wavemaster.
I've hit the regular Century Wavemaster before, with it filled with water. I pretty much put it on its side on the ground with each and every kick.
I've never owned or played with the Everlast freestanding bags extensively. The only time I've been able to play with one myself was at the store, when it was unfilled. But to be quite honest, it seemed really shoddy. I've also read that it comes apart sometimes.
Something I read once that may be a viable option for you, is to get the Century Wavemaster, spend the extra little bit of cash, and fill the base with some concrete. Then all you need is like a dolly to move it around. The problem I see for you with that is that to ever take it home from school you would probably need a truck or a sturdy car and a strong friend or two to help you load it up. You could also consider loading it with gravel or gravel and sand, if you can get it cheap/free. Just some thoughts though. All I can really tell you is that if you're any kind of power hitter, just filling one of those boys with water isn't really goin' to cut it.