It depends on what kind of environment you want - they're both excellent schools, but very different.
W&M has more of a traditional college feel, if that's what you want. GWU is much more urban, so you'll get less of the college feel, but of course you'll be living in DC.
Also, what do you want to major in? If it's something like international relations, then I'd choose GWU. If it's more liberal artsy, like English or History, I'd do William and Mary.
Good luck choosing. You'll get an excellent education at either.
