I actually have the Avalon Hill boxed-set version of RuneQuest, though I haven't pulled it out in a really long time, and I have a copy of Stormbringer. I think overall though, especially based on some of the things that have been said in this thread, BRP is the most attractive option to me because not only can it do fantasy just fine, but if for some reason he wants to start playing in another genre then we can do that while still keeping the same set of rules.
That's really interesting information about Ken Rolston. I had no idea the creator of The Elder Scrolls also worked on a BRP system. That's really cool.
I'll have to keep a look out for Magic World. Right now I'm wanting to buy BRP and Iron Kingdoms, and when Magic World comes out, I'll be adding that to my list too.
Thanks for all the great information!