you should have had a "Most of the time" option for the poll, I'd say I land rest 3 out of 4 times.
Mind games seem to be the way to go with puff. Bait those openings. Hop in like you're going to attack, but instead of attacking, back off(jump up, away, or over them depending on opponent and their habits). If you see an opponent that likes to shield, Pound that shield. if you do it right it's not easy to punish the pound, and pound almost breaks any shield, most of your attacks can finish it off, and the last thing opponents want is to be helpless against a jigglypuff.
Remember, Fair can Wall of Pain similar to melee's Bair, which makes it a little easier to perform than melee's version.
Uair can combo into utilt, which can combo into rest at low-mid %s. I think the latest I've been able to tilt/rest was... around 50%, although 40% is the latest you can reliably do it to characters around Lucario's weight(and 40% is the earliest you can KO with it on FD/omega stages without bad DI). You can still do it at a little higher %s but you have to double jump and your opponent might be able to answer it if they realize what you're doing.