On these servers, no matter how much you split up, you will form back.
NOTE: None of the XP earned from there transfers to your facebook/g+ account, because it's a private server, duh!
1. epeffects.de (disable your adblock before entering)
2. agar.io/?ip=vps56296.vps.ovh.ca:443 (can be laggy sometimes, my personal favorite) Moved to unnamedcell.com/ffa1
So, what is your highscore on these servers? It'd be my pleasure for me to know.