Last phone prior to GS3 was an iPhone 4.
It's hard to pick one thing I like most about the GS3. Screen is amazing and I really like customizing my screens.
I thought I would miss my pictures auto sharing since I use an iPad daily as well, but I don't. I use Drop box and I have not missed a beat.
I have been all over the place with phones in the last 2 or 3 years, from Blackberry to the original Droid, to iPhone 4, to BB 9930, to Droid 3 and then back to iPhone 4 prior to the GS3.
Every one of those phones did something very well. The only 2 that did a lot right were the Droid and the iPhone 4. However the GS3 is really amazing and so far it seems to do everything I need and more and do it very well.