I vote for both as well, its hard to lose money while investing in firearms if you use your brain. I own both and love both. The Garand carries history, practicality, great accuracy and shear knock down power, I've watched them double in price at gun shows over the last 5 years. And if you're just popping off rounds, .75 cent Walmart ammo feeds fine.
But in regards to the AR platform, my M4 is probably the weapon I "fondle" the most and is sweet as pie to shoot. It is endlessly customizable, upgradable, ergonomic, easy optics mounting, cheap ammo, less moving parts= easier to clean (unless you're a lucky SOB with a full auto) No recoil, lighter weight (depending on configuration)
The choice is yours, but as everyone else has said, M1s are finite. Even if someone starts reproducing them, they won't carry the history as the original ones do. ARs are a dime a dozen now because manufacturers wanted to sell as many as possible before the liberals banned them. Providing we don't give them a chance to ban, you should be able to pick up an AR for a while to come.
Brad