Hi Ryan-
Great advice given so far. I am going for as much of the set as possible and trying to stay somewhat in a VG to V/G-EX range, and trying to get a good blend of different backs in there.
If you are going for the whole set, you will need the commons just as much as the HOF'ers & the SL'ers. The commons are more affordable, and if you can locate tough front/back combinations for commons it makes it a little more exciting buying them (for me at least). I mix it up, since I need so many still I will pick up a HOF'er here and there, and then some commons. I'll probably wait until I'm over the halfway point before I start focusing on the SL'ers.
RobD. is right-if you aren't sure about whether or not you are in it for the long haul, HOF'ers are the best bet to focus on. And, Tony gave you solid advice about picking up groups.
Good luck hunting-
Sincerely, Clayton
*edit to add- +1 to what Jantz said* "Buy the card, not the holder"