I've heard them all including the Type X (Haven;t actually heard the Type E, but I know they are bottom end Alpine woofer).
The Type S is "ok" if your new to the whole subwoofer scene. (Approx 129.99 Retail)
The Type R is really good pending how you have it set up. They can pound very good and are a really good deal for the price. (Approx 249.99 Retail)
The Type X are the best. The ones O heard were 10'' (Haven't heard a set of 12's yet..) it was alittle of a over kill for the car it was in... they are nice though. (Approx 449.99 Retail)
All prices are Canadian Dollars and are PER subwoofer.