A counting system will only give you plus or minus a tiny bit of your edge ASSUMING perfect play. If you can play perfect and want that last little bit o edge, go for a harder count, maybe even a non ace reckoned count with an ace side count.
For some side bets though, learning counting systems for those decently could prove profitable if you run into them. Two examples are the 10 count for insurance and the Crush Count for O/U 13 (if you live in Europe

). Knowing about these might end up being useful, but as far was practicality goes they are limited only to their specialties.
For a general count (assuming you don't know if you are going to stick with it) Hi-Lo is obviously the place to start. If you think you might get pretty into it and have a general idea of the games you'll be playing, you'll want to choose a count better suited to those specific games. Hi-Opt II is fantastic for hand held games, something like Wong Halves or Zen works great at shoes due to the crazy high betting correlation (far more important than playing efficiency at shoe games).
Pick up some the the general books, they all teach various counting systems. Professional Blackjack and Blackbelt in Blackjack are two I just bought last week and have proved very helpful so far.
I decided to go with Wong Halves because I have mainly shoe games nearby and the extra level of difficulty (level 3 system) doesn't bother me much at all. You might decide that the slight edge this has over a level 1 (or the tiny tiny edge over a level 2) isn't worth the mistakes that will result due to your inherent skill set.
Try a few, practice with them, see what works.