I'm sure that either one would tackle what you are looking to do. My vote is for the .300 WSM, probably because I own a few. There is a large selection of both .7mm and .30 caliber loads and bullets, but the heavier .30 cal bullets carry more thump downrange. I've always liked .30s better than 7mms for all-around utility, though.
I also think that in terms of longevity and popularity, the .300 WSM wins. It is already the most popular, and that tends to help with availabilty of cases, components, and factory loads over time. Just my 2c!
PS- what action/barrel are you using for your project?