If you don't intend on using a Harris bipod or attaching weapon lights, then all you really need is an A4 style carbine from Armalite. It comes without a carry handle so you can buy one from them if you like.
If you want the closest thing to the real deal M4s, Noveske or LMT is the way to go. If you can find one, the Colt 6920s also work. All are quite expensive, but having "mil-spec" is expensive because mil-spec comes at mil-spec prices.
The M1A is an expensive gun to shoot. If you want to shoot with the accuracy of an AR, you have to pony up the money for a better trigger, bedding the stock, and also unitizing the gas system. I wouldn't recommend getting it scoped unless it's an M25, and if it is then feel free to scope away.
Both aren't going to be cheap unless you feel like going for a Bushmaster. If you don't need "mil-spec" then good choices also include Stag Arms, CMMG, DPMS, Armalite, and all of which are reputable manufacturers.
If you're getting an AR, make sure that you have an AR that has the gas-key staked right, unless you're a masochist or you feel like coming up with new lists of three and four letter words.
If you want to go the M14 route, definitely get the Scout Squad. The SOCOM II just gives too much muzzle blast. Building your own AR is going to need some armorer's tools if you aren't just getting complete uppers and lowers.
If you aren't going to shoot very far, and you're just shooting for groups and possibly using for HD, but you don't want to spend a lot of trouble building it, then the pre-built AR route is good.