Unless you are looking at an SKS-M or D model, you are talking two totally different set ups. The SKS is typically loaded from the top, with stripper clips, and has a ten round capacity, while the AK uses magazines and can use 5, 10, 20, 30, 40, and 45 round mags. (I think there's even some other capacities out there).
My first was an SKS, due to cost break-down, it was cheaper to get into, cheaper to shoot because nobody was doing mag dumps, and was more of an enjoyment purchase. Later I got into AK's, and they are a lot of fun too, allowing for a lot more combat set-up than the SKS (Yes, I know TAPCO and a lot of others make a whole bunch of stuff, but I prefer my SKS stock).
Since you say you have AR's, I would try to look at it as if you were deciding between getting another AR (hence the AK), or an M1 Garand (Similar to the SKS system in loading and use).
Or, with a typical ARFcom answer, GET BOTH!