I'd suggest you test ride both bikes before making any decisions. For myself, I've found in the past that aluminum bikes were a bit punishing on the less-than-perfect roads where I ride. Admittedly, I've heard that the latest generation of aluminum bikes are better. If you're on a budget, you might consider a used bike. Chances are that you'll get a lot more bike for the same amount of money. And when you decide that you need a completely different bike, you can always re-sell it without losing a whole lot of money.