Melo scored a lot of points. However, he was horribly inefficient and offered very little on the defensive end. I was a Syracuse fan in the 80s and 90s. It still misses me off that their title came with Melo. I have never liked him. Still, he should have been a Piston.
Howard was a great defensive player. He took the Poorlando Tragic to the Finals. Offensively, he was limited, but still put up a good amount of points.
As for the HOF, it includes all accolades, not just NBA. Even so, neither should be 1st ballot. I would put Melo in on the 3rd ballot at the soonest, Dwight on the 3rd or 4th.