I'd buy the .270 Win. You'll never have a shortage of brass and various bullets, for reloading. Also, perchance you went hunting somewhere and forgot your ammo (yes, boys and girls, it does happen), you'd be hard pressed to find a store out in the boonies that didn't have a box or two of .270 on the shelf. Also, it's a fine game cartridge, if you are accurate. If you're not accurate, then practice!
I've read several reports on the new .260, but don't know anyone personally who's shot one. I would wait to see how things shake out with it, before investing that kind of money in it.
JMHO.