S&W makes some great rifles! I have had experience with the M&P-15 and it was a great rifle to shoot, felt tight and felt like the proper time and attention was put into the rifle (gas key WAS staked properly lol).
However I have not had any experience with any AR-10's but I have heard they can be a mixed bag. Some are built really well (comes at a cost) others not so much (and still cost a lot).
I think the M-14's may be the better off the shelf .308 rifles. FAL is another option but its hard to find one that's not been Frankensteined.