The thing about aluminum frames (and I have one that I really love), is that they're more likely to get dented, and the dents will be bigger and perhaps more of a problem, than dents in steel frames. My steel commuter gets locked to a steel bike rack with steel locks - and it has a few small dents to show for it... if it were aluminum, there'd be a lot more.

So for ride quality there are much more important things to look at than the material; but for general toughness in abusive situations - steel has a definite advantage (don't get the thin walled stuff though!)