Many years ago before systems were given names I chose 3,4,5,6,7 as +1, 2,8,9 as zero, and 10,A as -1. The reason I chose 2,8,9 as zero is because in Dr. Trorpe's "Beat The Dealer" 2.8,9 out of the deck made the least difference. The most popular system however seems to be 2,3,4,5,6 is +1. 7,8,9 is zero. 10 and A is -1. Now tested at 51% playing eff. , and 97% betting corr. Whatever that means. The system I first mentioned is rated 55% playing eff. and 95% betting corr. Not enough difference for me to change.
Also I have added a side count of Aces to my counting, which means if the shoe is Ace rich I will up my bet amount a little early or also play a second hand early.
Speed Count is the easiest and fastest to learn. Two ways: first 5 is a +1 and Ace is a -1, count is balanced. Bet higher if count is plus. This system is balanced and no math involved in cards remaining in shoe. Play basic strat.
Second Speed Count method: Start with plus 4 or 5. Unbalanced system. The 4 and 5 count as +1. The Ace counts as -1. Bet units about 1/2 the count and play basic strat. Works easy to learn in a short amount of time, a day or two. Not as good as the two system first mentioned that may take 700 to 1000 hours of practice. In those system you vary basic strat. with the count. Has a lot more power, but more time to learn. If you want to be a pro build a good foundation.
Take what I say with "a grain of salt", 95% of the people who claim they are card counters are not.
I hope this helps.