As Jeroen said, more info would be handy. It sounds to me like he is a beginner doing white water rivverrunning, right? What he doesn't need than is any flatwater kayak, any composite boat or a full on creeker. So the range he can choose from goed from big river runner to playboat. Big river runners are relatively stable and easy to paddle, great for beginners, great for people paddling at the edge of their ability. The cath is they are not quite as fun to paddle on easier water as smaller boats, he won't be able to play arround a lot. I only have experience with the wavesport diesel myself, but most brand have a decent one. Playing is what playboats are for, but those are slower and get knocked over easier than the big river runners. Plus being 6' 4" and only 85kg he might have trouble finding one that plays well. He could try out the wavesport project or fuse, the jackson star or fun, the bliss stick rad or the fluid nemesis or flirt (my boat, great boat), all in some of the larger sizes. Since you said you were looking for an all rounder, this is probably not what you're looking for. Somewhere in between are the "normal" and playfull riverrunners, you'll notice when you see them that they are a lot flatter than the big river ones. Examples are the dagger GT and the eskimo Xeno (both a bit older, I'm not really up to date in this). [edit]O, and I forgot the fluid spice, not a bad boat either.[/edit] They're somewhat stable, and somewhat playfull. It's probably the best bet for someone who doesn't know what he wants yet. Don't worry too much about the confidence, it will come over time, especially ones he learns to roll.
If you have an idea which type of boat you're looking for than I'm sure there are some people here who can point out a few good ones for his size and weight. And don't forget, demo before you buy.