Re: I'm a young buyer looking into buying a decent semi-automatic rifle.
Well, lets see... an AK you can throw in a mud puddle, not realize that it slipped into that mud puddle from being stood up next to a tree, come back after taking a crap, pick it up and it will fire fine - it'll spit out some mud with the first couple rounds is all.... An AR will be a wee bit more temperamental in such a situation.. An SKS will generally just shoot forever even if you only clean it twice a year. So will the AK but the SKS is cheaper to buy. Then, you could go with a mini 14 - not quite the power as the AR but they each have their pros and cons. As home defense weapons they basically suck - as far as I'm concerned any long gun sucks for home defense unless you happen to be defending your home from outside your home. I stick with my .45 for inside home defense.
Now, if you want a semi auto rifle to simply shoot for fun, buy a Ruger 10/22 - you can shoot 500 rounds of ammo for $18 or less (I think my daughter just bought her last 500 round box for $14)
For a bolt action rifle - well, there are about a million different ones to choose from. The only rifles and shotguns I'm not a fan of are single shot varieties.
Me, I have my Marlin lever action 30/30 - use it for everything I need a rifle for - including deer and moose hunting. I suppose that's because I'm sort of a traditionalist in this respect and the Marlin fits well in a saddle sheath.