steel is a more comfortable ride because it flexes, but heavier than aluminium.
aluminium is lighter, so its easier to climb. but you feel all the imperfections in the road.
titanium is lighter still, so its even more easieer to climb, but the level of comfort is lower than aluminium.
overall, its lightweigh VS comfort/investment. steel will last forever and be comfortable, aluminium/titanium if ridden hard will fail and be less comfortable. its a simple payoff.
your choice.
im not saying steel is better. its really lovely to have a lightweigth bike, but it depends on what you use it for. my personal commuter is steel for duability and comfort, and my weekend speed machine is carbon. previously aluminium.
carbon is great on the road until it fails. then you have brocken teeth and wish you had a bike made of metal.