What server usually has the most players in the realm and not selling items?
I think US West generally has a realm at least mostly full if that is what you are looking for.
It’s not really too important to have the most players in a server, as long as there are people playing you should be ok on any server.
Even if USWest2 has a lot of people selling items, the realms are quite full. I know when I play on it, there are mostly 2 full realms at a time plus 2 more decently full realms.
USMW2 always has quite a few people on it.
Depending on your time of day I believe you will find the fullest non-trader servers at:
USWEST then when that starts to decline: AUS, then when Europe wakes up: EUEAST is the busiest.