Howard is a better athlete and better defender than Shaq, but Shaq was the more dominant player overall.
I mentioned in another thread that Orlando will be looking to get a solid player in exchange for Howard instead of just letting him walk and coming up empty-handed.
Miami could easily offer Wade or Bosh for Howard and the Magic would take that deal in a heartbeat, and it would be a win-win for both teams.
In my opinion even just Lebron and Howard alone would be much more dominant than the trio of LJ, Wade, and Bosh...