New to this, and I'm on the fence which to buy. Will be training for long distance riding soon. I'm looking at buying Giant brand, but not sure which will be better - carbon or aluminum. Thx!
I own both carbon and aluminum bikes and have ridden them for at least several thousand kilometers, but I think it'd be pretty much depended on what purpose the bike is made for. Even If your is a flagship carbon model and for racing, even used by UCI pro team riders, costs more than 5000 €, it could be a bit too "stiff" for average riders. Likewise, you can get an aluminum framesets that is indeed softer than decent carbon framesets.
So I'd suggest you try some of bikes the manufacturers claim as "endurance" or "comfort" models.
Carbon is always lighter (thus, requires less effort to move) than aluminum, and more confortable (since it's a bit more flexible).
If you can afford the price difference, hell yeah, go with carbon
That said: if price is an obstacle, aluminum will be just fine, and the weight savings on the frame is not as much as some will tell you (it depends on the actual bike and the type and amount of carbon fibers used)
If you are willing to spend up to $4000 then put titanium in the mix.
Opinion on durability of carbon varies. By many measures carbon is stronger and more durable than aluminum. But there are people that feel carbon is fragile and the right answer is I agree.
For race you are going to see a lot of carbon for weight.
Training is a different.
I like the ride (and weight) of a carbon but for my money aluminum.
You don't want to clamp anything on carbon so if you want to maybe mount a rack some day then no carbon.
Titanium is a little lighter than aluminum, more durable, and has nicer ride. Aluminum will fatigue. You can mount a rack to titanium. Could also use the bike for light touring. It would not be called an endurance bike but it would be nice for long distance training.
If you are willing to go up to $4000 then clear the field and don't limit yourself to Giant.
For long distance training you could get a very nice aluminum for $1200. Maybe even consider used. It is going to take some long distance training for you to know what you want in a long distance training bike.