Ok, so my opinion is based on the [Dub] found on DisXD, so Pardon if I seem behind.
Lillie: She's elegant, and draws a lot of screen time. I suspect that there's gonna be some plot later that thrusts her in the spotlight. Already she's acclimating to things and learning not to be such a wallflower, but that's not without it's advantages.
Lana: She's quiet and sweet like Lillie is. Of course she's a lot more confident in herself, and it's apparent. I honestly felt like some moments starring her felt forced, outside of the plot where she spends time bonding with her Popplio and training it. She shines in moments with Pokemon and it shows. Not so much around people.
Mallow: Whoa. Wow. She's like a female Ash. She's outgoing, exciteable, fun and most of all quite motherly and very impulsive. Like Ash she's also a Force of Personality. She really has her own thing. I haven't seen anything developing her character much though, and she's due it. I know she's onscreen quite a bit, but it's always supportively for someone else. Want to see some real Mallow to Shine. Haven't seen any yet.
Sophocles: Hehehe. Cute. Togedemaru just drives home how young he is. You don't see a lot of Pokemon who are quite as evidently feminine as Togedemaru is. It's a refreshing thing to see. Especially since she just happens to be a hyperactive ball of cute. I get the feeling she's young too.
Kiawe: Dependable guy, seems miles ahead of Ash. Seriously, someone get this guy a freaking stamp or two. Maybe he just overcommits himself, but definitely a gentle rival for Ash. I'm so glad this time a possible rival isn't a douche nozzle like Gary or Paul.