Some commutes are like long training rides with safe storage at each end. Others involve hacking around the urban jungle, hauling groceries and locking the bike up in a public place. These are two very different styles of riding.
Steel and Al are both suitable materials. My steel commuter road/touring bike weighs the same as an mid-level Al hybrid.
The alleged "harshness" of al frames is not relevant to shorter journeys and they all seem to be strong enough.
Ti is generally too expensive and stealable for a utiltiy bike although every other characteristic makes it ideal.
Carbon lacks the surface toughness so it can be damaged by careless handling and the daily dings that a commuter bike has to accept.
The design of the bike is far more important.