The AK-74 is the same design as the AKM-47 stamped receiver rifle, only modified slightly to lighten it as much as possible. Mechanically they're the same.
The basic decision is: 7.62x39 or 5.45x39. Each has advantages.
The 7.62 is currently more available in more bullet types. You can buy new Russian made commercial ammo or American made commercial ammo including sporting ammo with soft point hunting bullets.
The 7.62 is better for hunting larger game, being about equivalent to the old .30-30 Winchester.
The 7.62 is a shorter range round, with more recoil.
A loaded rifle will be heavier.
All the commercial ammo is non-corrosive.
Military surplus is corrosive primed, and is getting hard to find.
The 5.45 has some Russian made sporting ammo, and Hornady?? is selling an American hunting bullet loaded in a Russian steel case.
It's available in military surplus corrosive ammo at CHEAP prices. A 1080 round sealed steel can sells for less then $150. which is the cheapest surplus ammo around. Buy plenty of it and you can have a lifetime supply.
The 5.45 is very effective as a small game and varmint round and is effective on smaller deer.
It's VERY effective as a defense round due to the infamous tumbling bullet.
A loaded rifle is lighter.
It's a flatter shooting, more accurate, longer range load than the 7.62 and has extremely low recoil.
The top of the line in either caliber is the Arsenal conversions of the Russian Saiga rifle. These conversion are as close to a Russian full-auto AK as we'll ever see.
The Arsenal SGL series is available in 7.62 and 5.45. Price is usually above $800?? but it's the Cadillac of current AK's.
These rifles have hard chrome lined barrels and chamber.
All you have to do with corrosive ammo is to use water or something that contains waster to flush out the corrosive salts residue, then clean the rifle as normal with bore solvent, etc.