Zoro and Luffy definitely got the most hands on training over the timeskip, being mentored by two of the most skilled people of the previous generations.
In that regard, they got very similar teaching, but in terms of what they learned, there is a clear cut difference.
From what we’ve seen of Zoro’s time training, Mihawk took a very hands off approach when it came to teaching Zoro.
From this flashback we can tell that after learning the basics of Haki, Zoro was told that there was a step beyond and that he wouldn’t be allowed to drink until he mastered Armament of the blade.
Rayleigh was much more direct with Luffy, as we can see from the multiple flashbacks. Chapter 894 shows a flashback in which Rayleigh is using a haki-coated wooden club in order to increase Luffy’s proficiency in Observation Haki. However, he also used deprivation to motivate Luffy, through challenging him to dodge 100 attacks before he gets to eat.
Now to compare the two. In a basic summary, I’ll say that Rayleigh was much more basic in his teachings, but cemented the basics better and clearly defined how Luffy could grow, while Mihawk taught Zoro more advanced techniques, such as extending his armament coating to weaponry and increasing the potency of his sword slashes.
We see Rayleigh told Luffy about the advanced levels of Observation and showed off Advanced Armament himself.
Meanwhile, I’d say that Mihawk taught Zoro more advanced skills, but the fact that Zoro was confused when Gyukimaru told him that black blades are forged through battle indicates him not knowing how to advance his skills beyond where they currently are.
I’d say the personal dynamics between the student and teacher also played a role.
Rayleigh and Luffy became close over the two years, and I think Rayleigh really wanted to help and teach Luffy all he knew because of how impressed he was by Luffy’s character.
Mihawk on the other hand would have maintained a very formal relationship with Zoro, since at the end of the day, they are still enemies who would eventually fight for the title of World Strongest Swordsman. I think Mihawk didn’t really involve himself in teaching Zoro like Rayleigh did to Luffy, but instead let Zoro figure out things by himself. The wound Zoro got on his left eye might be a result of him sparring with Mihawk and trying to force himself to learn a new skill.
Another aspect is how much of a power difference Oda wants between Luffy and Zoro. Obviously right now, Luffy is far ahead by learning Advanced Observation Haki.
I believe that Zoro would also eventually learn these techniques, but the question remains as to if and when he will figure these out by himself.