Pretty self explanatory. I have a Floatzel on my team, but her very crappy accuracy Iron Tail is the only coverage against Fairy types I have. Looking up other Water types, Octillery gets both Flash Cannon and Sludge Bomb, which are quite good, as well as other really nice moves. I just caught an Alpha Octillery. But I've never heard anything about whether Octillery is decent or not. Even if it isn't good enough for competitive, is Octillery a decent choice for an in-game team? And before you mention Empoleon, Piplup was my starter in Shining Pearl and I explicitly made it a rule for myself before both games came out to not make the teams too similar (the only shared Pokémon is Luxray).
Octillery, in my opinion is better in this case because no only does it have a equal attack as floatzel, it has a higher sp. Atk as well a better move pool. While it’s speed definitely doesn’t help it, agile style is able to somewhat help with that. If you still wanna pick floatzel, I would recommend aqua tail, iron tail, ice punch and crunch. We as with octillery I would pick hydro pump, flash cannon, flamethrower, and psychic/sludge bomb.