Like 99% percent of questions on BF, the answer to the question is "IT DEPENDS."

I think you need to tell us more about what your goals are, what type of riding you do, how much you weigh, what your budget is, etc. for us to give you good feedback.

And don't get started on the whole tubular vs. clincher debate, that's another can of worms!

I do agree that all things being equal (rim depth etc) carbon is lighter than aluminum. But it's not as strong, so you don't really start seeing carbon rims (or carbon/aluminum hybrid) until you get deeper section (say >35mm).

Anyway, unless the OP give us some hard info on goals and riding style and whether these will be race-day only or "everyday" wheels the masses are just going to spout their drivel.