I ordered my HOX without actually demo'ing it and though i love it I have been curious about the S3. Well, my local ATT store just got them in and I was able to play with one for about 15 minutes. Honestly its a nice phone but I though the screen was was too dim even at max brightness and thought the Touchwiz interface was ugly and slow. There was a HOX right next to it and I kept opening the same apps at the same time and the HOX seemed faster time after time. Played a few youtube vids side by side and honestly the HOX screen is just that much better. The one thing I did like about the sammy was the loudness, the speakerphone, media volume and earpeice volumes seemed significantly louder on the S3.
I think I would have chosen the HOX even if I had the chance to compare them before I bought, it just seems more cutting edge and representative of a flagship phone. Now if only HTC would fix the volume issues on the HOX.