I want to buy my chappy a kite for xmas - we already have mountain boards which we've only had a few months.
He's no experience with kites but I know he wants one - which is the best for starting out. He weights about 13.5 stone. Obviously he'll have to learn to fly it before venturing on the board but ultimately needed for pulling him along on the board. I've read alsorts of reviews most of which contradict each other

Depends on what you want to do with your atb. If you want to cruise, go with the bullet, if you want to start getting air eventually get the blade. Avoid the stacker. At his weight, I would start with a 3.5 or 4.5 bullet or a 3 or 4m blade. You can learn on these, then make them a higher wind option later down the road when (notice I say when, not if) he gets a bigger kite. I personally would go with the blade, but I love the lift.

Scoop

Basically the Blades will pull you upright, good for the boards, whereas the Bullets give a lot more vertical pull, ideal for buggying.
The other option is to go for some budget kites and get more of them - you can get 2 Busters/Beamers for the price of a Bullet/Blade but you do get what you pay for...
for boarding it may also be worth looking at the Begos, they give loads of lift :D