When you select your characters, do you care which order they are in? Assume that (for the purposes of this poll) position-based colour tanking is not a concern.
How much do you care who goes where?
Assuming PVP whomever you want to tank goes on the left. Position order is the tie breaker for match damage. If you are playing PVE tank goes middle, left, right.
Game Mechanical concerns aside, if I’m using a character who’s known as a leader (e.g. any version of Captain America) or for being particularly aggressive (Daken, Rogue), they go in the center. If I’m using anyone who’s a notable support/backfield character (GSBW, Bucky), they go on the right, in “back”. Otherwise, it’s more or less just in the order they come up as I scroll through the team selection screen.
Re: Option 3, I always like to have Grocket out front in that combo. I mean, once they’ve laid out their Strikes at the start of the fight, it doesn’t usually matter what happens to them, so I might as well put them where they’re most likely (even if only by a tiny margin) to soak more damage.