Seaking and Arcanine for me. I'll be honest, I don't often use fire types. The only three I've ever used before Reborn were Blaziken, Typhlosion, and Delphox, other then that I saw them as a waste of my time. But by the great Lord Arceus, Arcanine is a monster. He's gotten me past every single major challenge to date, from the PULSE Abra and Arceus to Charolette's team. Even more surprising is the fact that I ended up with a modest Growlithe when I rescued the police officer, so I'm not even using Arcanine's attack stat in these battles. Though his Special Attack is through the roof.
The other one is Seaking. Once again, I don't really use many water types, and generally I stick to Gyrados, but Seaking is turning out to be surprisingly useful in battles. I found that Seaking did amazingly well in most battles and is a good utility pokemon, what with it having Waterfall, Dive, and Surf. Seaking even gave Charlotte's team a good run for her money.