I personally prefer alums with my Trad bows, but use carbons with my compounds. The reason is as McDave said above.
With Trad bows the arrow is tuned to the bow via arrrow spine (length) & adding weight up front, where with the compound's adjustable rests & draw weights the bow is tuned to the arrow.
In many if not most situations you can get a closer starting spine with the length you want for a Trad bow with an alum. Alums tend to be heavy enough that you don't have to add extra weight (brass inserts or weight tubes)to get an acceptable overall weight, as is often the case with carbons.
Alums are by & large cheaper than carbons, which may or may not affect your decision. I find them much easier to work with when fletching and tuning broadheads, and if I bend one I can often straighten it in a snap (I have a pro shop model straightener)....