Maybe it's got something with having been born after the AR/M16 platform was adopted by the military, but I lean toward the AR-10. Eugene Stoner is indisputably the greatest gun designer of the 20th Century. Props to Mikhail for making the most common rifle, and of course without John Moses Browning we might still be using lever-action rifles (maybe).
Yet at the same time, I can't get away from the design that Patton hailed as "the greatest battle implement ever devised". I can't help but wonder if he would have transferred that honor to the AR-10, had he lived long enough. My first dalliance with the Garand action was a Ruger Mini-14, and I loved it. Had the chance to lay fingers on an M1A in my LGS and while it was a smidge heavier than I thought it would be, the M1A was RIGHT. I love old wooden stocks... They invoke images in my mind of the rifle on display over the fireplace, walnut gun cabinets with walnut-stocked rifles inside, a warm, organic feeling when you're holding it.
Yet I'm at heart a practical man. I know that wood swells, and no matter how well-bedded the barrel is, the stocks can affect your aim in extended outdoor situations. For that reason, my preference is synthetic stocks and handguards, and the absolute utility of the AR platform for customization, accessories, and the endless supply of aftermarket parts makes it the preferred choice. Optics? No problem! No need for special optics mounts like with the Garand/M1A/M14 design. You can personalize the AR with literally anything your heart desires. How can you beat that?
Two eras. Two rifles. Each one has its place, and it's a bit like apples & oranges so I'll take one of each thank you!