Well obviously most of the pokes here have flaws.
Celebi: Weak to a lot of trappers. Easy setup for a few pokes.
Latias: Weak sort of to trappers but sub makes counter trapping easy but not amazing coverage.
Abomnasnow: scizor beats it as it can see if abomnasnow will focus punch switch to a poke who can take it then kill as it'd have lost its sub to u-turn. Also hail does nothing really for us and in a way benefits them and Kyurem.
Skarmory:rotom-w can counter it no problem and is easy to counter. Also I think skarm is better at setting up spikes as it gets more free turns but again easy to counter.
All in all I think the psychics would be best as they can beat all of team 1s pokes in some way and are sort of difficult to counter. They also can escape the trappers as latias can sub on switch to scizor and then as latias switches the sub takes pursuit damage magnezone gets a free switch in and celebi can baton pass/u-turn. Yes abomnasnow can sub but hail is actually bas for us.