I used to be into the chromoly flywheels over the aluminum ones. Now I've kind of reversed my opinion mainly because with the aluminum ones you can simply replace the friction surface instead of the whole flywheel. Basically they're both good.

ACT just came out with a line of chromoly flywheels and the pricing is pretty good right now. Check out the page at Options Auto, they run from $224 to $251 depending on weight which is one helluva deal.