@ Mike,
When I asked what you wanted your AR10 type for, I was meaning what type of mission you want it to fulfill. In my instance, the primary mission for all of my rifles is: long range precision competition (i.e.: 1000 yard matches), secondary mission being hunting (where legal), and tertiary being a SHTF go to rifle. For my desire, I would require (at a minimum) a 24" barrel, preferably a 26". Different missions require different characteristics. For example: I have my Colt HBAR as a NRA Service Rifle, my 24" AR was built as an NRA Match Rifle for NMC matches, my 26" barrel AR is the basis for a 1000 yard rifle, and my 18" AR is for plinking, introducing my children to the AR, and for CQB home defense.
An M1MkII is a converted M1 Garand. In the late '50s and early '60s, while the USMC had adopted the M14, the Navy had mounds of M80 and M118, plus a burgeoning supply of M1 Garands. The Navy inserted an adapter disk into 30M1 barrels, allowing the Garands to fire the 7.62 NATO round. These Garands were designated M1MkII, and were inventoried aboard ships, mostly subs. The downside to the Navy modification is that the adapter disk would sometimes eject with a fired round, going back to 30M1. The Navy Marksmanship Unit capitalized on the conceptual idea, and built their National Match Service Rifles out of M1 Garands rebarreled with match grade barrels with true 308/7.62 NATO match chambers. (I have two Garands, an early Springfield still in 30M1, and a Korean War vintage Harrington and Richardson converted to 308. I find that the 308 Garand is easier to fire in rapid fire stages than the 30M1 Garand.)
The conversion to an M1MkII is actually easy and cost effective. For the first few years that I shot my M1MkII, I never had the mag well block, so all it took was the cost of a Kreiger M1 barrel, and having the chamber cut with a 308 reamer.
I didn't offer a suggestion either way between a Ruger or a S&W for two reasons. First, I am not familiar with either specific product, and second, neither offers a variant that comes close to meeting my personal mission parameters.