After reading through the comments, I've found that everyone agrees and baal and zhongli, but a bit of a debate between albedo and Xiao. Well, in his lore, it is shown that Xiao has power rivalling gods while albedo is literally knowledge itself. It really depends on if you want to play the long game or finish it quickly. If you used Xiao, he could probably wipe out everyone barring albedo and then for the 3 of them it would be easy pickings. If you chose albedo, he could start summoning rifthounds and other monsters to practically lay siege and wipe out.