If you sell the SKS you'll get a whopping $150 to $200 for it, I'd personally just keep it as a spare.
You never know when a spare rifle might come in handy.
The AK puts out more rounds as it's got a detachable mag that lends itself to spewing out rounds at a high rate of fire. Even with a higher cap mag than the 10 round mag it comes with the SKS can't throw out that many rounds or be reloaded quite as quickly as the AK, but the SKS is usually more accurate than the AK is. At 100 yards groups from the AK will almost always be 1/3 to 1/5 larger than groups from the AK using the same ammo, by the same shooter and under the same conditions. The AK will just bang out more rounds than the SKS will in a shorter amount of time.
My point is that you aren't really going to gain that much by selling it and it's a good solid rifle and at some point it will come in handy. A buddy may need something to use on a hog hunting trip, your brother doesn't have a gun and wants to borrow something because something comes up or maybe your AK breaks, is stolen or is unavailable for some reason then you'll be really glad you kept it around. They aren't making any more of them, the price on them will only go up and some day gun stores won't have them for sale at anywhere near the price you sold it for.