They are all good but I don't want Sara since she is the leader of the Legends and Clark has not been character developed enough. Kate could be a leader in the future cuz she is experienced with everyone the least. I see John being more of a leader than Barry.
He's kind of an amalgam of the best iterations of Clark Kent and they've established all those traits in past episodes of Supergirl. So he's developed enough. As for Kate, this version of her hardly was experienced.