Depending on the matchup, bait and punish is generally better. With characters that are avle to just sit and camp you like Villager, Duck Hunt and some other guy, rushdown is generally a better option as if they are one one side and you are on the other, they have all the room in the world to use unsafe moves. If its someone like Fox, Zero Suit or Mario, bait and punish are geberally better. The bait and punish style is harder but is much more effective, as it requires you to get into your opponents head. For uairs, the problem you may be having is you say strings, they shouldnt be strings, they should be a combo where your opponent has no way to get out of then during it. The best way to consistently do it is playing with real people, because while bots will always DI the same, people wont (hopefully). This is also why the bait and punish game is better, as it helps you learn how your opponent will DI. If youre new to Meta knight going into training mode and practicing on a floaty (persobally I found Lucina to be the best) is helpful to start, but since the patch the uairs into shuttle loop is not as easy. Paying attention to percentage is also very important, because you will wither need to react to if you uair again in the combo, or if you have to end it with another move. Around 20-30 percent is when it is easiest to hit all 5 uairs on an opponent, past around 50 however it is difficult to go past 3 depending on the character they are playing. Sometimes if they fall through bait an airdodge nd hit them with a dair. If shuttle loop will cause you to sd, do one less uair and use you last jump to finish it with a nair. If they di out left or right, hit them with a fair or bair. Uair is an extremely powerful tool, but it is mostly learning how to effectively use that tool that makes it strong. 4 percent a hit isnt that useful, so learn its other uses than just racking up percent