right now there is not much difference between official and private server.
I think the only difference are
Official Server:
Cash shop is cash shop
Many Items in the mall
Updated server
No(Few) Bugs
Readable quests
Active GM
Minimum downtime with notice
normal rates
Private Server
Cash shops can be bought in vis/feso
Few Items in mall
according to rndbit, he will not update the server
Buggy
I dunno the language they used
NO GM AT ALL
its down when rndbit is asleeep
x10 rates
LOL as i can see.... official server is now better so think again