I vote Emiya, ngl, the guy knew what Saber can do and her weakness, he will do everything to take the win, even it is dirty sniping tactic, 1 vs 1 he probably can't win again Saber, with 2 vs 2 Emiya has alot of option, such as constantly sniping Stelle to force Saber from either choose to protect Stelle but couldn't get close to him or abandon Stelle to go for a close combat with him. Assuming we have Holy Grail War Command Seal with Master-Servant link, then Rule Breaker is ready to counter that. In case Avennturine being the target, Emiya sniping protect him, he did that in UBW against Berserker, where he constantly sniping Berserker as a mean to both attack and prevent Berserker's advancement when the big guy fighting Saber, he can fire multiple homing arrows at once sniping both Saber and Stelle isn't a problem, and since it is homing arrow, they are forced to block, the only reason Lancer counter Archer was the guy have Protection from Arrow allow him to dodge projectiles, or projectiles will automatically miss
So all and all Archer take this, he is versatile and have multiple ways to deal with this match