The military type gun I would like to have is a .50 caliber rifle. That is pretty much the biggest and most powerful weapon you can get easily and legally. They are very expensive though.
An AR15 is ok because they can use high capacity clips and are accurate and durable. The Ruger Mini-14 is cheaper than an AR15. I'd get a Mini-14 Ranch Rifle ($600-700) over an AR15 because they are less bulky and are easier to break down, clean, and remove/fix jams. Another even cheaper option is the Kel-Tec SU-16, at around $500. It works with AR15/M16 clips and breaks down easily, plus it can store an extra 30 round mag in the stock. I've read its more accurate than a Mini-14 out of the box. All of these are .223 caliber, which is great for long range self defense, but not for hunting anything bigger than varmints.
As for the AK-47 like SKS, I wouldn't buy one. A friend has one and he says its junk.
Personally, I'd invest in a big gun before getting one of these, but I already have a semi-auto .30-06, a lever action .30-30, and a bunch of semi-auto .22s and a couple of shotguns. lost, in your shoes, I'd probably look for a semi-auto rifle, either the Ruger or Kel-Tec. Then you can spend the money you saved by stocking up on ammo. No gun will do you any good if things are really bad and you run out of ammo.