I have an option to join one of 3 teams. My initial thought was to join the color team I liked best, but is there any advantage to joining one team over the another? For example, do I get different rewards when leveling up or anything?
Items are equivalent. The factions are only there to separate the player base, so that people can compete / work with each other. The important things to consider are:
What factions have your friends joined?
What factions are dominant in the area you play in most?
Do you prefer to play for the dominant side, or would you rather play
for the underdog?
Worked the same way in the predecessor of Pokémon Go, Ingress. In Ingress each faction had lore, but in Go there does not seem to be any backstory whatsoever as of yet.
Alright so there seems to be certain icons/logos for each faction that represent one of the legendary birds (Zapdos for Instinct, Articuno for Mystic, Moltres for Valor). Maybe in the future some change or patch will come that will do something with the birds.
Also note that when first interacting with a gym at level 5, a short description is given by each faction leader.
Instinct is basically all about the intuition and ‘hatching‘ of Pokémon.
Mystic is interested in researching the ‘evolution‘ aspect of Pokémon.
Valor is pursuing training and improving the ‘strength‘ of Pokémon.
Perhaps in the future, bonuses of some kind are given for each faction in each of these aspects. Until anything has been confirmed this is still, of course, merely conjecture.
Source : Link , Question Author : Dragonrage , Answer Author : Codestrife