You can pretty much find nice people everywhere, but aswell you'll find ******** everywhere. Its Flyff, and its not like it been back in the days. The Scene became salty over time and tend to be in a negative attitude.
While saying this i do definetly want to clearify i dont wanna make you not wanna come back to flyff, there's some servers worth playing, some rather not, it depends on your taste of gameplay, let it be highrate, lowrate, pvp or pvp based.
Its hard to give you a good hint on where to luck by the short info's you gave us
I personally do not play Flyff so i might be one of the best to tell you which i personally think are worth playing (as actual players would just suggest the server they play on by the fact that they want to raise their playerbase.)
Server's i liked the gameplay on:
Highrate: Forsaken, Insanity
Low-Rate: CW (even tho i dislike seasons, and the way that their staff is handling users is quite painful either but this is based on just the gameplay.)
Other Servers worth mentioning are MoonFlyff, EntropiaFlyff and probably Spirit Flyff. Euphresia might be quite nice too. (These ones arent much 'played/tested' by me so better check them out urself xD)