If it had to be a true "Ranch Gun" and not just a popularized name for a toy; then an SKS is definitely a great choice. The 7.62x39 is a much better choice in caliber than a .223. (I love my AR15's - more than one: But the .223 caliber is not the be-all of all calibers.)
But having worked on a ranch here in Wyoming, I wouldn't go with the SKS or any semi-auto if you truly wanted a ranch gun. (Ranch gun to me, means a WORKING GUN - too much dirt, mud, etc..). It's on your horse or ATV if you use that for working the ranch. You're not talking about going coyote HUNTING, which means trying for a 200 yard shot. It means you need the gun for something you weren't looking for. If I was buying a ranch gun, I'd buy a 16"-20" level action 357 magnum. It can still take coyote and deer out to 125-150 yards. You can shoot some really hot ammo in it and do some pretty decent hunting. Ammo is not that expensive. $20 for some good 158 grain lead rounds (You can get cheaper). SKS ammo is about $15 for the same amount of ammo. But for plinking, you can also shoot 38spl in it.
Magazine capacity is around 9-12 depending if it's a short 16" all the way to a 24" barrel, and depending on the make of the rifle. Either way; more than enough ammo. (This isn't a SHTF red-dawn rifle - It's a ranch rifle).
Anyway; I'd rather have a rifle that if it was going to get bounced around and actually used, that I wouldn't have to worry about dirt getting in the magazines. NON-detachable magazine. The lever action is nice and sealed and the perfect ranch gun. "After all, that's one of the reasons it was built". I wouldn't go with the 30-30. I'd go with the 357 magnum. For what it's worth, they also make the rifles in 44 magnum. (Which allow you to shoot 44 special). Also 45 long colt. I like the 357 magnum, because I also have a 357 magnum revolver. I can swap ammo back and forth. (Very popular among ranchers and such). If you owned a 44 magnum, I'd choose that caliber of the rifle.
P.S. Didn't see Smaug's post prior to posting mine. (Still waking up). Great minds think alike. A real ranch gun; not just a "Name" needs to be lightweight, effective to 100-125 yards. Obviously the SKS is fast, and would even be effective; but whether it's a removable magazine or a top loader magazine, there will be issues with dirt. (If it's really a Ranch-Gun). A tubular magazine is so much better all around for this type of application.