Andrew Bynum seems to have more offensive skill than Howard, but Howard is the better defender. Bynum has never been a defensive player of the year like Howard has. Both Miami and the Lakers have gotten better and OKC have not gotten better in this off season.
The Lakers have done a better job of making up for their shortcomings. The Lakers needed a better point guard, better defense, and a better bench. They were able to address all of those things during this summer.
The Heat needed better big guys, but they weren't able to pick up any yet so far. The Heat have gotten better with Ray Allen and Rashard Lewis, but these two guys don't really address the Heat's problem with defending the paint. We'll have to see what happens in the future as more trades can still go through.