I would never say you'd regret an aluminum bike, as there are many that are great, comfortable and affordable. Carbon is a want, not a need.

Folks here rave about the Cannondale CAAD 10 and it's definitely a solid bike. You also can't go wrong with a Giant Defy. You should be able to get both with a 105 groupset for under $1,500. Specialized bikes are fine, but I don't have much experience with them. Just looking at comparable models, their price points seem to be a bit higher than the other brands, but every manufacturer has different names and it's hard to easily do side-by-side comparisons.