Ive owned three Banshees. They are a ton of fun, but require just as much maintenance and care as any other quad. A Banshee is water cooled, and comes stock with two carbs, so it is more complex than a Blaster. They are very reliable if taken care of. I like the brutal powerband and raw power, but a Blaster is more fun on the trails because of their small size and better (with aftermarket suspension, anyways), handling. A Banshee is very fast in a straight line, but in stock form they feel clumsy.
Hope that helps a little. Id love to have another Banshee, but its not worth trading my Blaster away to have one IMO. If you get a Banshee, be sure to do a compression test, and look carefully around the engine's drive sprocket area for damage to the cases. Banshee's are notorious for throwing chains (because people don't take the time to keep them lubed and properly-adjusted!), so chain damage can be present on lots of used 'Shees. Be aware.