Morakniv. Cheap, sharp, decent steel. I personally prefer the carbon steel blades as they're harder and hold edges better. But their stainless ones are fine too and less maintenance. They're easy to clean. The more complicated a knife is, the more time you spend getting dried blood out of the nooks and cranny's. Plus, Mora's are so cheap, if you lose it, it's not really a big deal. I have a few nice knives, but I take my Mora's hunting most of the time.
Spend a while learning how to sharpen. It can be frustrating at first, but after a while it will be second nature. You shouldn't ever have to sharpen in the field. Make sure your fixed blade is sharp before you hit the field. You should be able to field dress 3+ deer before you see any significant edge degradation on a decent steel.
I never liked the idea of replaceable blades...just doesn't make sense. Sure, they're super sharp, but they're not going to last long because they're thin and (obviously...) designed to be replaced often. Which means you have to keep buying blades...no thanks. A good fixed blade will last you decades.