If you hit the button twice it should put the shard with the most players online at the top.
Edit: Sorry it has been awhile since I have opened UO, I guess I had SA stuck in my head for a moment, percent full and connection put the "lesser" answer at the top, and Time zone puts the "greater" answer at the top. So fo %full you should get oceanic, for Connection you should get the server that is farthest away, and for time zone you should get the server closest to you.