Probably Jiraiya because first off I cried when he died. Also the emotion Naruto showed when he died and all the flashbacks just showed the strong emotional connection. They were one of the best comedy duos. Also Naruto would have been pretty much lost without Jman
This is a bit difficult. First let's list out all the things that these mentors taught Naruto:
1. Tree climbing
2. Chakara nature (which led to the development of rasenshuriken and its variants such as lava style rasenshuriken or bijuudama rasenshuriken)
1. Water walking
2. How to call on Kurama's chakara to an extent (at the level that he used against Neji)
3. Summoning jutsu
4. Rasengan and how to make bigger rasengans
5. How to release basic genjutsu
1. Sage mode
1. How to attain KCM
2. How to use chakara arms
3. Bijuudama (Bee taught Naruto the 8:2 ratio which Naruto almost got during training and later perfected when he got bijuu mode. This subsequently allowed Naruto to even use variants of bijuudama such as super mini bijuudama)
Despite the quantities on this list is difficult to pick a best one since each one gave Naruto something that he would have been lost without
ohhh wow lema..a other biased opinion...(we all know why u chozed killar B)..
1-jiraiya teached naroto sage mode and rasengone...and spended long time of training wit him..jiraiya was like father to naroto and not just semsei...
2-killa B train naruto for small time...but korama still not obey naroto...teh only reason why korama obeyed naroto and start work with him is when madara show up in a battlefield..