>>30023354They play completely different roles, so it's not that easy to compare them.
Mantine pretty much counters any non-HP Electric Keldeo thanks to its increased HP and newly gained Roost, whereas Pelipper just became the first weather setter that also has a momentum move (U-turn). Also, Pelipper can abuse rain really well with boosted Scald and no-miss Hurricane.
Overall, I'd say Pelipper is better. 
