Both Private Servers and Official Servers are good, iRO uses it power to make players think that Privates are better, even if it isn't all truth, while privates try to make iRO look bad, and it isn't truth either.
iRO is a good server, I have to say, even if the rates are too low I still like it, I say I would be playing if I had enough time/money to play it, but since it is too easy to acess, most f*** in the world can be there, it isn't that bad, but still annoying to bump into scammers and nerds on steroids. About the server, it isn't laggy, it is actually good, GMs are too busy helding over nine thousand bot spamming the support sistem and trying to help the players, they can't do events when they are so busy. WoE is aways good, so populated and full of guilds, even with all castles open, there is like 1k guild in the server to WoE on 30 Castles, so it is aways competitive.
The server is outdated because they just update when they fully test it, to have no really bug in it(If people doesn't remember, there was a lot of abuses every update it had, until the team changed), I guess they also wait the green light from kRO, but when added it is fully stable.
On the other hand:
Private Servers are all of above but customizable to your own will.

So you can get a updated or a not updated version, a laggy or not laggy server, a friendly or a competitive community, a small or big WoE. You just need to learn scripting.