I can vouch for Warloria being reasonably popular.
The average when I played was around ~90 actually, probably had a lot more over-seas players such as myself!
Anyway, I have theforbiddenworld.servegame.com - ~60 - 80 players online from the Oceania region at any time.
If you Google "the forbidden world OT", the top hit is our wiki that I put up 3 days before I had to close the server haha.
I also had chaosisles.no-ip.org, wasn't up for more than a month and don't really recall the amount of players (wasn't huge, the above db had thousands of registered accounts...) but might be worth something to ya.
I don't know if you need to me to vouch for my own credibility (being a low poster here...) but you can check me out @ OTF:
View Profile: STiX - OpenTibia Fans
PM me either here or there if you are interested.
I won't let theforbiddenworld go too cheaply, as it was pretty big back in the day and I'm still getting offers to buy the server as a whole (despite deleting it quite some time ago), but I might get the urge to start it back up again.
ChaosIsles feel free to offer what-ever you think is fair. TFW, however - don't offer anything too insulting please, but I will be up for negotiation.