None are bad... They're just all situational. PK Flash can do some pretty good edgeguarding pressure, and if it hits, man does it hit. But it's pretty safe at least. Warlock Punch has some super armor frames now. With a good read, rest in peace. Heck, I'm pretty sure Ganon can take a Falcon Punch and not flinch if you time it right. So it's good as a counter of sorts, or reading some landings.
Backslash is the most reliable of all, though, because it's fairly fast and has great range. You can generally hit with it multiple times a match if you use it well, but it's not really going to be very rewarding unless you get the back hit, and it's also risky. Landing the back hits though, is much more situational and requires good prediction, but he has some good setups for it like B-throw or using it on an opponent above him or punishing landings from behind with it.