Kimmimaro no doubt

Guy, Tsunade (sannin war), Hinata, Neji - reason/already in the late level and i still use em, depending in the situation (9tails, survival, ninja exam, etc)

Hinata/Naruto/Kimimaro - key to a lot of hard fights and ninja exams as f2p, and are good in general.
Sasuke/Anko/Haku/Yamato - essential for 9 tails with matching main until you get rare barrier ninja.
Kabuto/Tsunade/Guy/Kurenai/Neji - good free ninjas that can still be used at high level.

In my opinion, some of the best free ninjas you can get are as followes

Kimmimaru - Excellent tank and mystery and does decent damage

Hinata - She has awsome combos potential, causes accupuncter and is an excellent tank. She is useful for Ninja Exams also, really help with some of the harder ones where you NEED to stop DPS from coming through.

Sasuke 3* - One of the few ninjas with 3 chases, good damage, has a barrier and can cause ignite. He single handedly makes a ton of combos work.

Kabuto - Excellent heals, can make clones ot soak hits and do some dps and he buffs curse mark ninjas, like Kimmimaru

Guy - Ignition chase, buffs tai damage and gives leech, has an interupt and solid damage.

The Akatsuki - Can grind these guys from the various shops. Sasori IMO is the best one to go for.

Kankuro - Full team AoE that applis poison, puppet does good damage and can tank and ignores guarding passives.

This post was last edited by 101***@facebook at 2017-1-11 23:06

In my opinion, Kimimaro, Sasuke and Hinata/Neji is my top 3.