The good stats you want to keep and want to reforge are usually the main stats such as Ninjutsu, Taijutsu, Critical, Life, Damage Reduction, Defense, and Resistance.

The secondary stats that are pretty good is Injury, Control, Combo (depending on your team and ninja). Ninjutsu *ion is also great as secondary stats.

I would still focus more on the main stats rather than secondary so you can switch around ninjas without much hassle.

~Jib