So, here is an informed answer, cause it seems like you have not gotten one yet . I have played with both phones a lot, and i own the GS3. Its all gonna come down to preference in small areas.

The Razr Maxx HD. Price 299.99
Huge battery. Charge once a night and be totaly fine. Might be able to get 2 days out of it on very little use. Gorilla Glass screen, stomg kevlar ( or however you spell it) on the back feels really nice. The phone its self is heavy, but not a brick. Software wise just a little below the gs3. The biggest difference is the 1gig of ram the HD has conpaired to the 2gigs the GS3 has.

GS3 Price, 199.99
That 2 gigs of ram is amazing in this phone. the screen is nice and bright and responsive. Ive read multiple reports on the glass on the front on the screen, Samsungs website doesnot say tis gorilla glass, but lots of reposts do. Ive put an email into samsung to get a direct answer. i dont have the balls to put a razor on my screen without fully knowing. I do have a portable charger for my GS3, but im a heavy user. Expect to possibly have to charge this phone throughout the day.

I went with the GS3 because chargeing it while in my backpack is not a problem for me. I love the speed of the phone, and with the slim case i have on it i feel good. Im not horribly rough on my phone. Hope this kinda helped you. GL