A lot of it depends on your price range and what you're looking to keep for the PC. I've had some really good hits out of Classics this year, but most of those have been of the older veteran/retired players. Threads is just ok - even though they've added a 4th hit in the box, most of those have come in the form of a $4 free agent rookie autograph. SPx is pretty nice if you like lots and lots of rookie materials. Each box of that stuff I've opened has has either a triple jersey of a nice patch card as well. A bit more expensive than the others mentioned, but a LOT of fun to open. Topps Chrome is decent for a low end product, delivering quite a few base RC's and refractors, but the autographs are pretty tough. With only 1 per box, you just hope it isn't one of the third-round tackles...
So my recommendations would be Classics or SPx, depending on your budget and RC vs. Veteran PC needs!