Well, Kakashi is a genius and an advanced level instructor. Naruto was a total zero in terms of skills and knowledge while being extremely immature at that time so he did not have a material that was workable. On the other hand, Sasuke was ready to learn advanced knowledge and techniques and reminded Kakashi of himself who he wanted to save from a dark path. Then again, playing favouritism at that time definitely affected Naruto :( though he came to understand why Kakashi did it and did not mind it any attention later in story.
Naruto needed to grow as a human being before being trained as a ninja. That was what Jiraiya’s training was all about. Sure, he was not the most mature person ever when he returned back from the timeskip but compared to Part 1?! There is way way too much difference.