I was doing fine in the IF PVP with a core team. After a few matches I started mixing it up and varying the team I used and now I have no idea what team someone who finds me in a node will face. I am referring to just the ‘best’ team someone who stumbles across you in a node will find, not a retaliation.
Is it possible to find what team your are fielding?
Not without external communication. You would need to know someone that could queue you in your slice and have them check to see what they see.
I would like to know what the “stronger” team means. For example, in Simulator, I played a bunch of different teams:
277 Invisible Woman, 271 Elektra, 186 Hood
275 Hulkbuster, 272 Jean Grey (4-star), 185 Cyclops (3-star)
271 Iceman, 229 Kingpin, 189 Iron Man (3-star)
276 Wolverine (4-star), 229 Cyclops (4-star) 187 Iron Fist,
276 Wolverine (4-star), 188 Deadpool (4-star), 199 Mr Fantastic (best part - it won the match. 
Which one of those teams would be the one that other people face. My feeling that the “strongest” would be the Hulkbuster/Jean Grey/Cyclops team, but who knows? By levels, though, it’s the IW/Elektra/Hood team. Any guesses?
From a CS response, the team with the greatest number of levels. That would likely mean the first team.
You also need to account for “significantly weaker team.” If your second winning team is weaker than your first but not significantly weaker then I believe the second team will be your defensive team even though it is not your strongest team.