Either way we always recommend you have a boom made from monocoque - single shell - construction so that carbon versions will be as stiff as possible and aluminium models are still strong enough to cope with any forces the metal is under in extreme conditions.
In some cases it's hard to argue against carbon. For example, when using powerful, cammed slalom models (especially in the larger sizes), then a ‘soggy’, flexy boom will lose all the extra power you should have on tap - and have paid serious money for.
Other riders, such as a some of freestylers you will see, prefer a slightly more ‘absorbent’ feel to their rig.
ENERGY EFFICIENCY - DIRECT OR FORGIVING?
For many casual freeriders an enjoyable time on the water can involve energy saving thanks to the flex and forgiveness an aluminium boom delivers.
For others, the more direct the connection the easier it is to channel the power of the rig and allows longer sessions – and more fun!
It really is just a matter of personal preference to ensure you're having the most fun possible!
Go and try both and see which you prefer!