I've been using Wong Halves doubled since 1980. It goes; 1, 2, 2, 3, 2, 1, 0, -1, -2, -2. The BC is 99.3% and the PE is 56.4%. Actually, back then I assumed that "bigger is better". Since then, blackjack simulation software has shown this to be basically true -- but to a rapidly diminishing extent as count complexity goes up. Wong Halves outperforms Hi/Lo by about 8% to 10% with about double the effort required. Still, I continue to use it because I'm a dinosaur and am very used to it.
I probably wouldn't suggest that a new AP learn Halves. Something like the unbalanced KISS III (96.3% and 55.2%) is very adequate and requires maybe 30% of the effort. For somebody who wants near optimum performance, the level 2 balanced Mentor Count is very good at both shoe and hand held games (97.0% and 62.2%). Neither uses any side counts.