Best trainer.

[The Gambler1981]

To me there is no such thing as a best trainer, at least in an overall sense because fighters are so different that no one could have a way to good work with all different kinds.

There would be a best trainer for a specific guy.

I will say this though the guy I see the most of is John David Jackson, if so many guys are going to him there must be something to what he brings to the table.

[Ray Corso]

I doubt you'll see what a trainer knows by watching one fighter in a few fights. First off he needs a student that has some ability to first absorb the lessons then be able to carry out the techniques!
What the best trainers do is accentuate a fighters positives and try to eliminate faults that could cause him being defeated round by round.
Angelo Dundee was very good at getting the best out of a fighters best attributes and masking the fighters weaknesses.
With my statements in mind I think Abel Sanchez does a great job "preparing"
fighters to get into shape, work on methods tailored for opponents, then getting them ready mentally.
He has the best facility and you'll notice a lot of trainers will send their fighters to him for prepping!
A great trainer needs to find and develop great fighters to begin with, that's the hard part. Developing a young kid to become a great fighter is a constant battle with the "streets" and you loose far more than you win and the best talents don't usually have will to sacrifice.
the best I know of;
Mr. Blackburn
Dundee (before Ali)
Petronelli Bros.
George Benton
Eddie Futch
Johnny Davenport
Jimmy Montoya
Pat Nappi
Me....................hahaha and a few that I'm forgetting.

I had a few really good ones but I would have loved to have worked with guys like Pete who was high skilled and had all the coordination skills in the ring you could possibly need.
Ray Corso

[ShoulderRoll]

Did the Petronelli Brothers produce any champions besides Marvin Hagler?

And which fighters did Jimmy Montoya train?

Just curious.

[Sugar Adam Ali]

Obviously it's Ray Corso

[Resilient]

Robert Garcia or Freddie Roach.