If you buy factory ammo, go with 30.06 - it's the most common, easy to find ammo out there. I'm talking Wallyworld & gunshops - not the internet. If you're going to roll you own, buy whatever suits you & load the cartridge you like best. My 300 dollar Marlin XL7 30.06 will kill anything in North America, no need to get fancy or expensive unless you enjoy that.