Out of the ones in the US, can’t decide.
It depends if you want faster party-finding and dungeon-queues, or slightly less lag and shorter getting-into-game queues during peak hours.
Orsha has slightly fewer players and proportionally more BR players. I’ve had very few problems not being able to communicate with people around me and, besides day 1, the queue to enter game has not exceeded 100 (less than 10 minutes) for me.
I also played on Klai for a couple of days. The queue often exceeds 100 so you can expect a decent wait, but more people once you get in.