It depends on the character I'm fighting, honestly. If I'm fighting somebody with a good recovery like Rosalina or even another Pit / Pittoo, I'll usually let them ledgesnap and then punish them on the getup - if I'm feeling particularly daring, I'll try go for a ledgefall aerial to catch their recovery's linear trajectory as it's about to touch the ledge; on the other hand, against somebody with poor air speed and recovery like Ganondorf or Ike, I can usually suffice with arrows.
Point is, it's all contextual. How you apply off-stage pressure will inherently depend on the nature of the opponent and how they can recover - there are even anomalous cases like Ness (can be super easily gimped with arrows or a well-timed f-air, but the risk is massive if he connects PKT2 before you get to him) or Olimar and Duck Hunt (decent recovery, but very easy to catch as it comes). I like to mix it up depending on whom I'm fighting, and occasionally throw in a new trick so I am not predicted.
Some techniques I find useful and which can be applied essentially universally are:
- Arrow baiting. Charge an arrow (use the rotation method if you need to store power) and then release, aiming for your opponent as normal. If they read it and airdodge, you've now set them up for punishment. Get stuck in immediately after they airdodge and f-air them, repeating it necessary.
- Arrow nudging. If your opponent is very close to the blastzone and only needs a slight tap to get KO'd, a charged arrow can push them back just enough to get the kill. I think it's easier to do this with Pit's arrows, as you can aim them to a greater degree and the knockback is the same as Pittoo's.
- F-air is always a good tool for chasing your opponent in the air. It can string together into a Wall of Pain combo that can efficiently drag the opponent into the blastzone - again, though, it depends on how good your opponent's recovery is and how they can DI out of your combo.
- D-air should honestly only be used as a last resort or mixup. If you do it too often - as in, your go-to reaction for edgeguarding is to go for a d-air spike - your opponent will read it and react accordingly. It's very predictable and honestly seldom worth it as a spike unless you have expert timing; opponents like Pit / Pittoo and Rosalina, at lower percents, can even recover back to the stage with little effort. D-air can be a great damage-dealer, though, and if you have good timing and the opponent DIs accordingly, you can combo d-air strings for high damage. It probably won't kill in this way, but it can be a good setup for a f-air or b-air if you can connect. Condition your opponent into airdodging or expecting something else, then go in for a d-air spike if you feel confident and want to shake things up a little.
Pit is a champion at gimping and off-stage play, it just takes a bit of practice. Never be afraid to go deep: Pit's recovery is fantastic and you'll almost always make it back to the stage safely, and whatever trouble he may have killing on-stage, off-stage is his zone.