Now my first choice would be to get him the rc8 rtr buggy from associated. This is a great buggy and he will have great fun with it. I know he is nine but spend more now and spend less later is what I go by. As we all know he is going to gget hooked and the two buggies you mentioned before may not last him as long as an rc8 or 8ight. Also if you are set on one of those too go to your lhs and see what parts they carry. Also see if you can buy it threw them because if you dont they will be half as likely to help you when your son breaks a part which will happen eventually. Betwen those though I would get a hyper seven because its proven. I have seen them run and they can keep up. The only thing is get him a better radio and also defanately change the steering servo out. There are some great deals in the for sale section of this sight on servos and radios check it out. Whatever you get just go with it and have some fun with your kid!!!