re: Battle Rifles
I'll try first.
AK-47:
Advantages: Legendary reliability, cheap ammo (as low as $90 for 1000 rounds), dirt cheap 30 round magazines for as little as $5-10 each. Easy to field-strip with no small parts or screws to get lost or misplaced.
Disadvantages: Mediocre accuracy, not very attractive looking (like that really matters).
Prices start from about $250 for the Romanian SAR like I have to near $1000 for the Russian originals. I really like my AK as I think it offers the best balance of magazine capacity and caliber. Plus, it works!
AR-15:
Advantages: Very low recoil, lightweight bullets so more can be carried given weight limitations, very accurate, good sights, fairly easy to field-strip (pull out 2 disassembly pins and you separate the upper and lower receivers, then just pull bolt assembly out), magazines not as cheap as AK but still reasonable ($19 for Thermolds, $25-30 for GI demos, $50+ for Colt factories)
Disadvantages: Gas system supposedly lends to fouling and thus subsequent jamming problems, .223 round seems somewhat anemic compared to other 30 caliber rifles, prices start at $600 to well over $1000.
Note that I have had no problems with reliability with my Bushmaster AR in about 160 rounds. I really like the lightweight and design, but the caliber sort of turns me off next to a 30 caliber gun. That said, if I was "stuck" with an AR, I would not feel undergunned.
M1 Carbine:
Advantages: Very lightweight (about 5 lbs), cheap magazines ($10 for 15 rounders, $20 for 30 rounders), almost no recoil, good reliability (so far with 100 rounds), disassembly is like your Mini 14.
Disadvantages: Expensive ammo, difficult to find ammo sometimes, 30 carbine round is basically a 357 magnum in a 110 grain bullet.
Aside from the pistol-like cartridge it fires, I am so far a big fan of the M1 carbine due to its lightweight and controllability. However, because of the caliber, I would probably opt for a "real" battle rifle before this.
M1 Garand:
Advantages: Powerful round in 30-06, surprisingly low recoil, great lineage (I believe General Patton called it "the greatest battle implement ever devised".
Disadvantages: At 9 1/2 lbs it's no lightweight, hard to find cheap non-corrosive ammunition for it, the en-bloc loading system can ruin your day if your thumb gets caught in the bolt when putting in the clip.
I have only put about 40 rounds through mine, so I cannot fairly judge it. I like the round, but hauling that thing around would get pretty tiring and the 8 rounds it holds pales in comparison to the 30 round magazines of other rifles. But, considering it was good enough for our GI's in WWII, that should say a lot.
SKS:
Advantages: Same ammo as AK, good reliability, 20 and 30 round magazines are still availiable, uses stripper clip loading.
Disadvantages: Many come with fixed 10 round magazines and trying to change them can be a pain in the a$$.
Personally, while I like the gun, in my opinion, anything the SKS can do, the AK can do better.
I know you said you did not consider pistol caliber carbines, but how about a semi-auto UZI? I have one that takes 9 mm and 45 ACP and it is very reliable and easy to maintain (just unscrew barrel, take off top receiver cover, and pull out the bolt). It may not hit as hard, but hi-caps are still availiable and what could be more politically incorrect than an UZI?
I hope this helps, but I'm sure people far more knowledgable than me can do much better.