I preordered a 32 blue, to keep unlimited data. The S3 is a better device in all areas except for a few things. I have had 2 dropped calls at my house on the Samsung while I had none on the Thunderbolt. Also I didn't like the music player and dropped $5 for Poweramp. The last thing is the email program, there is no way that I can find to keep emails from being deleted from the phone without leaving them on the server (I use a pop3 email). I used to like having a copy of all of my emails on my phone, I found it very convenient when I was travelling and had to talk to a client and reference an email they may have sent me.
Other than those issues, everything else is better, screen, battery, ICS, etc.
Also, I use a non-stock keyboard, which I also did on the Tbolt, if I remember correctly, I didn't like the stock keyboard on the S3.
I've had a few people comment on how nice the screen is, I could feel the screen envy from an iPhone using friend of mine.
Enjoy your new phone, you made a good choice.