Hmm... Let's compare.
Sucker punch hits if only your target is actually trying to put out some damage on you. Sometimes, you fail if the other Pokèmon is not attacking, like if he or she uses Recover, Lightscreen, ect. Or any non-damaging move.
Covers: Ghost, Psychic
Fake Out hits on the first turn ONLY. If you use it on any other turn other than the first, you fail to use the move. Although it makes the target flinch, a Steadfast Lucario could KO it with Dak Pulse or something...
I would really recommend Sucker Punch** for your Meowstic instead!