This question is impossible to answer, yet I have people ask this all the time. My answer to this question is what ever round you prefer. Though if I had a choice to chosing a rifle closest to the AK-47 I would go with the 7.62*39mm, on the other hand if I wanted a rifle closest to the AK-74 I would choose the 5.45*39mm. Also don't dis-credit the .223 (5.56*45mm) because its not an orginal AK round, it is a awsome cartridge.

Again another question that is impossible to answer. It depends on if your going to go plinking or going to compete in matchs. Since I dont compete I usally use Wolf brand ammo(its steel case). AK rifles eat this stuff like candy, its cheap and performs well too.

The steel cased rounds are usally cheaper to produce then brass cased, thus the ammunition cost less. Though one should be mindfull that the lubricating lacquer can get messy. Make sure you clean your rifle once home from the range because the lacquer can build up possibly causing a jam( common in high tolerance rifles such as the AR-15, its not a big problem with AK type rifles). Don't let this discourage you from purchasing this type of ammo though, many militarys around the world used this type of ammuntion.

The brass cased rounds are usally more expensive to produce but are less messy, and can some times be reloaded. With AK type rifles usally the steel case is used more often, but most match grade and hunting cartridges use brass. If you like to reload your ammuntion then brass is the only way to go.

Full Metal Jacket have a metal jacket, usally made out of brass that encloses the core of the bullet. FMJ rounds are designed more for penetration then expansion. The Hollow Point round on the other hand is designed to expand rapidly causing large wound ballistics. The rapid expansion is caused by the hollow air cavity in the front of the bullet filling up with a water like substance(such as flesh) forcing the bullet to mushroom. Current NATO laws forbid the use of Hollow Points in combat because of the massive wounds they can cause. To sum it up FMJ rounds are better against body armour then HP. On the other hand HP rounds are better against non-armoured soft targets then FMJ rounds. This is why they are used in hunting more often then FMJ.