I would suggest any real real mountain bike, they have mountain bikes by huffy, but they are mountain bike styled, when you look at the detailed information they say rather specifically that they are intended for road use only, not trails or off road. Then better style bikes, like mongoose, as you head up the line, are considered true mountain bikes, but mongooses shouldn't be used for jumps or downhill unless specifically designed for it.
So I would recommend any mountain bike, but remember what you pay for is what you'll get, if it's a hundred dollar adult mountain bike styled bike, then you'll have a 25 dollar hunk of metal with a 400% markup.
Steel is the best bet, don't do aluminum.