I have two different StarterCharacter models (both humanoids), I know how to make a single StarterCharacter the default to spawn as (place it in the StarterPlayer folder).
What I'm not so sure about is how to make it (for example) if you are on red team, you spawn as one character, and on blue team you spawn as another.
I don't want you to give me a script that points to a certain Player ID, I have the humanoid models in studio.
Sorry if this sounds confusing and I think this is the correct forum, if not please let me know :)
Ben posted the answer on comments, so I'll write his answer here.
Put both in the StarterPlayer and name each one to their team names and then make it so that it changes the name of the model of the team you're on to "StarterCharacter"