Aluminum should be fine. It may or may not last 20 + years, or perhaps you'll be ready for an upgrade before that time. I'd rather have a non-rusting frame for commuting.

Some brands of aluminum frames are susceptible to corrosion and salt damage though. Just ask your vendor about the warranty if you are purchasing it new. And, of course, it depends on your environment.

Also consider the used market (without warranty). You can often get a better bike for the same price, or the same bike for much less. Of course, a lot of used bikes need a good tune-up depending on the seller.

If you're riding longer than say 10 mile rides, also consider drop-bar bikes.