How does it compare to the Galaxy 3?
Well the Thunderbolt is a year and a half old, its specs are much lower than the S3. I definitely think you would be much happier with the S3.
The 'bolt had a bunch of software bugs that were never worked out, and still doesn't have ICS, which the S3 has stock.
True. Newer isn't always better, but I'd love something running Android 4.0 stock.
The S3, being newer, should have more support as well.