well I would say without a doubt ar-15. several reasons for that. First let me say the Garand is a great gun that I hope to own eventually, but there is a reason I went for the AR first. Lets see, cheaper ammo, available hi capacity mags, an incredible variety of customization options, and, well, one heck of a cool factor too. I would love to get a garand and will in time, but for all practical purposes, AR all the way.
unless of course you are shooting from a trench..