Once upon a time, all bike frames were made out of steel. Consequently, all the newer materials used for constructing frames of compared to grand daddy steel. The newer materials are lighter than steel, but are not as strong.
To adjust for the differences in material, the tubes that make the frame are larger, which changes the geometry of the bike. The materials feel differently to different folks, depending on what they want out of bike — speed versus comfort. If you're shopping for a road bike, it is important to ride a bunch of bikes from different manufacturers and different frames. Consider it research. As Renée Gaumond of Left Coast Cyclery puts it "There is a bike out there for everyone. You got to get out there and ride different bikes and see what feels right. Trust your instincts. "
To see a thumbnail comparison of the materials, just
|Aluminum||Lighter than steel frames 1/3
|Large tube size
Can feel harsh on long rides
Makes for a bumpier ride
|Steel||Rigid decreasing energy wasted with bike flexing
Some say they can't feel the road
Harder to find these days
|Carbon Fiber||Light weight
Makes for a smoother ride
Can be manipulated into exotic shapes
|Can break easily
More expensive than aluminum
|Titanium||Lighter than steel by 1/2
Strong as steel
More flexible than steel
Can be difficult to repair
What do you ride?