So what are you planning to do besides gaming?
If you're planning to do CAD work or other software that you know is multithreaded then i'd go with the FX 8120, you'll see better results. For standard things like web browsing or just other random little peices of software then i'd probably drop down to the cheaper Athlon II series of chips, granted if you could spend a little more i'd probably go pick go with a Core i3 chip, but you would need a new board.
If you have to pick between only between those two then th Phenom II X4 would probably be the better fit for just ''playing around with lots of apps''. I'd only go with the 8120 for more CPU intensive things needing to be done.