I've owned one for just less than 2 months. It's an excellent phone; fast and smooth.
Unfortunately it's stuck on Gingerbread 2.3.6, and according to TracFone, it will not be upgraded.
I posted questions about upgrading on Twitter, to both Straight Talk and TracFone, until TracFone finally answered. (My questions and comments probably annoyed them after awhile.)
I thought I kept their response but I didn't.
Frankly, all I really want is to root it but I've tried a half dozen methods, with no success.
I have a Droid X on Ice Cream Sandwich, and a Nexus 7 on Jelly Bean. I'm cool with Gingerbread 2.3.6 on the Galaxy SII. Just want root to block ads.
Hope this helps.
Edit: to answer the question, no, I would not buy the SII again. I'd get an unlocked SIII and use it on Straight Talk.