Best Team for Pokémon Sun

Incineroar

Fire / Dark — Starter

Litten's Fire/Dark typing handles Grass, Bug, Ice, Ghost, and Psychic types throughout all four islands; Darkest Lariat is an extremely reliable STAB move against Trial Captains.

Wishiwashi

Water — Schooling Tank

Wishiwashi is found near Brooklet Hill early in the game; its Schooling ability transforms it into a massive school at HP above 25%, giving it the highest stats of any Water type in Sun.

Vikavolt

Bug / Electric — Special Attacker

Grubbin on Route 1 evolves to Charjabug at level 20; Vikavolt's Bug Buzz and Thunderbolt provide excellent coverage and it arrives just before the final trial.

Mudsdale

Ground — Physical Tank

Mudbray is found at Paniola Ranch after the second trial; Mudsdale's Stamina ability raises its Defence by one stage every time it's hit — excellent for tanking totem battles.

Toucannon

Normal / Flying — Physical Attacker

Pikipek is on Route 1 from the very start; Toucannon's Skill Link + Bullet Seed and Beak Blast give it surprisingly powerful physical output for a Normal/Flying type.

Kommo-o

Dragon / Fighting — Late-Game Sweeper

Jangmo-o is found in Vast Poni Canyon near the end of the game; Kommo-o's Dragon and Fighting STAB coverage hits almost everything for solid damage.