Hey I'm from North East
Surely, I would love to help you out in this. Almost every state's of North East is best to visit but I have visited these state's so I'm suggesting you -
Assam: Guwahati, Sivsagar, Tezpur
Gangtok Meghalaya : Shillong, Jowai, Dawki, Cherrapunji
Arunachal Pradesh : Ziro Valley, Mechuka, Roing, Pasighat.
Nagaland : Dzukou Valley , Dimapur