What is the best treatment for mononucleosis?

Mono. Really is none. Rest, fluids can help. Acyclovir (anti-viral) may speed up recovery, but not a great deal. Vitamins can be important.
Rest & good nutritio. There is no special meds for mono. The treatment is supportive & situational. Those who play contact sports or ride horses or bicycles should not do so if they have an enlarged spleen.(trauma can lead to rupture) appropriate rest and proper nutrition should allow the body to heal as fast as possible.In adults it can take weeks.