Hi-Lo is perhaps the easiest card counting system to learn and play in real-time, but it is good enough to beat the casino in the right game. These days, beating the multi-deck game is tough! IMO, I think it's a much tougher game then trading profitably.
The more complex systems, like the one Ken Uston played, where he assigned different values to each card and counted aces separately using his feet only provided a slightly bigger edge, but that system requires more time to master obviously. As I mentioned in a previous post, you can't make many mistakes or you will eliminate the small edge that card counting provides.
More importantly is the deck/shoe penetration before the shuffle. In a multi-deck game, the edge is gained towards the end of the shoe. If the penetration is poor, meaning the dealer shuffles with 2 or more decks left in a 6/8 deck shoe, that is probably an unbeatable game. Also, good money management, proper betting given your bankroll, increasing your betsize according to the count, and the game rules, such as doubling down on any two cards, doubling after splitting, surrender, 3 to 2 Blackjack payout, etc. are all important.