gus said:
I mean, I know how they works but, is in fact one better then the other ?
Without knowing more about you, the answer is no.
Hi-Lo and KO have a very fundamental difference: Hi-Lo is a balanced counting system (the number of "low" cards equals the number of "high" cards) and KO is an unbalanced counting system (there are more "low" cards than "high" cards).
The big advantage of an unbalanced counting system is that you don't need to convert from the running count (RC) to the true count (TC). Because of the imbalance, at a certain count (known as the pivot), the RC equals the TC. As the RC moves away from the pivot, it becomes less accurate (which is the big drawback of an unbalanced count) but if you choose your pivot wisely, the unbalanced count will be as accurate as a balanced count in all the right spots (generally between a TC of +1 and +5).
The big advantage of a balanced counting system is that there are alternate techniques - Wonging out and shuffle tracking - which are only possible if you can do deck estimation.
If you can very easily estimate decks, balanced counts are more versatile with the same effort. If it requires a lot of effort, or if you can't divide by 2.75 very easily, unbalanced counts give the same results with less effort.
You should pick the one that works best for you, and don't worry if one is 0.0000001% better than the other. Being able to keep the count without forgetting is 10000000x more valuable than picking the mathematically best system.
gus said:
The only difference between the two is the pivot. The pivot for the Red 7 count is +2, the point at which you first gain an advantage on the house. The pivot for K-O is +4, the point at which you first gain a big advantage on the house.
If you play all with a very large bet spread, K-O will probably be better than Red 7, because your most important decisions are near +4. If you Wong in with a very small bet spread, Red 7 will probably be better than K-O, because your most important decisions are near +2.
Again, you should pick the one that works best for you. If you get confused with red sevens and black sevens, it's worth more to adopt a count that you can keep rather than trying to squeeze the extra value out of the perfect system.