if you could have one ninjutsu.

[TheBattousai]

FTG. It's one of the most versatile ninjutsus in the narutoverse. It can be used offensively, defensively, and even for leisurely traveling.

 

[Lankeysob]

Shadow Clone jutsu, would be nice to be able to have my clones learning different things and have them assimilate all the different knowledge for me.

 

[knowledge561]

Between Flying Thunder God and maybe Contract summons. To be honest I'd be happy with normal ninja abilities. Fast speed, jumping through trees, taijutsu like a boss.