Get whichever you like, and tweak it how you want it. At this point, there's just as many do-dads to slap on a AK as there are for an AR. Texas Weapons Systems and Parabellum armaments are your two choices for a top-rail cover for a scope. The latter also is working on a prototype HK-style non-reciprocating left sided front charging handle for the AK (replaces the gas tube, and probably the gas piston).
In terms of bleeding edge accuracy, an AR15 can be made to be very accurate. In terms of AE Black Box or XM855 in an Colt 6920 vs a 5.45 Saiga with surplus 7N1, you won't see much difference, other then ammo cost, and the saiga needs to be washed out with a garden hose after shooting (corrosion prevention).
A lot comes down to what you want to do with your rifle: Is it going to be a weekend range plinker shooting soda cans and washing machines? Are you going to hand load and try to print that perfect 1/8th MOA 10 shot group? Something to keep behind the back seat of the truck? Or something to keep stashed away for a rainy day? If you want bleeding edge accuracy, naturally go with an AR. If you want a plinker, either will suit you fine, truck gun? I'd go with a saiga, and rainy day? I'd invest in property and camping gear myself.