The 4th upwards variation is the best for killing at center stage (around 155 (at the last hit) for midweights). At the ledge, the forward variation kills around 120. The full downwards variation is the best for racking up damage. It deals 20 damage, but the opponent can DI out of it the easiest and if the do, they have might enough time to set up a trap. It's fairly safe at midlevel play; I haven't used it against top level players. So use the downwards to get 20 percent on For Gkory, but be careful in larger tournaments. Also, don't use the downwards 4th hit on Bowser. His Tough Guy ability means he won't flinch. He'll stand and grab you while you use it, so always go for an upwards finisher or a forwards one on Bowser.
If your opponent sheilds your Dancing Blade, you have two options. First up, you can stop the combo (if you play it out normally,they can punish). If you stop the combo, it puts you and your opponent about even framewise. In other words, you should be safe, but you'll need a quick get away.
Your second option involves mind games. You can stall Dancing Blade, leaving time in between each hit, and end with the downwards finisher. This will leave your opponents sheild VERY low or might even break it. If it's low, you can B reverse your sheild breaker in the air and keep applying sheild pressure. If your opponent stops sheilding as you stall your Dancing Blade, well, they get hit and you quickly finish it off with the finisher of your choice.
All in all, I use Dancing Blade and aireals and jabs until they are around 60% or near the ledge. If they're near the ledge, you can try to edge guard depending on who your opponent is, or if they're at 60, they can DI out of the downwards variation. At 60, i switch to almost exclusively aireals to try to space them and push the to the edge where i use jab -> Forward Smash to get a kill (Forward Smash probably won't kill at 60, but by the time your aireals push them to the edge, it could)