Either should do fine. I have a couple of Sig pistols that I really like and given the right price and the right specs would buy a Sig AR. That being said, I did the same thing in comparing the Sig 716 to the Ruger SR762. I ended up with the Ruger based on four criteria, the lighter weight of the Ruger, a nice factory carry bag, three Pmags, and I liked the factory front hand guard. The dislike was the sorry trigger, which was helped by polishing and eventually replaced by one of the new Ruger trigger/LPK kits that are now out. The accuracy is outstanding and is probably better than I can shoot. Reliability has not been an issue especially with the later serial numbers (56104500 and up s/n). As far as parts, I believe both will give you the same options as far as after market parts including a milspec buffer tube, standard LPK, SR25/DPMS mags, and 5/8x24 threaded barrel. The 7.62 BCM Gunfighter charging handle will fit the Ruger. Most of the other parts (upper/lower receiver, bolt assembly. forward handguard, etc) are proprietary. My advice would be to go and handle each, check the price, and buy the one that trips your trigger.