Froakie and Frogadier don't get many good level up moves and require a lot of TM use to be good until it evolves into Greninja, which is really good due to both of its super strong water and dark type STAB access.
Popplio is probably even worse with Liquid Voice, because it's only other coverage move in the form of Disarming Voice is turned into a water type move and has to wait until it reaches level 15 for Icy Wind and level 44 for Moonblast. But by then you will probably have a ton of TMs to use on Primarina, which fortunately has a good moveset.
It doesn't really matter which you choose since they're both going to blast things away with STAB Water moves, but I'd choose Froakie, since Protean is the superior ability as well as an ability to beat both Incineroar and Decidueye with its STAB moves. Be careful with how frail Greninja is, though.