I've used both but I prefer KO because it is so easy to use. But Hi-Lo is more powerful. Here is a comparison of the two.
8 deck, S17, Das, 1-10 spread, 60 hands/hour, 75% pen, $10,000 bankroll
HiLo Il18,Fab4 $5.54 per hour
KO prefered $4.89 per hour