What are you looking to spend?

Aluminum is light, cheap, and stiff. Carbon is more expensive, but doesn't transmit vibrations the way that aluminum does. There is also some issue with frame geometry--aggressive aluminum frames seem to be a smoother ride than the relaxed ones. My current bike is aluminum and I just did a 50-mile ride, with about 20 miles on chip-seal. That was...unpleasant. But on decent asphalt, it's fine. I've ridden three carbon bikes, and only one of them actually fit, so I can't say much.

Compact double vs. triple. There's a lot of discussion on that subject here. I've been using a triple, but a lot of the bikes I'm looking at use a compact double. It's hard finding anything other than entry-level bikes with a triple, these days.

Test-ride a bunch of bikes and use that to make your decision.