There are many ways to do many different things. It's safe to say that any action can be executed in a multitude of different ways. So what exactly makes one way the best way, the most preferable way, or even the least effecient way? Does it come down to a matter of opinion? Maybe because it's always been done a certain way? Perhaps there is an actual science that proves it. Whatever it is, and all answers could be right for different actions, there are hundreds of ways.
I could go on for hours about the best way to dress, the best way to talk, the best way to travel, but instead it seems more appropriate to discuss the best way to train.
How can there be a 'best way to train' when I just said there are so many different ways to do practically everything? That's simple. The best way to train is to appropriately train for your goal. Now, the training program might not be that simple, but training for your particular goal will be the best way to train.
Let's assume, we want to achieve 20 pull ups in a certain period of time. You aren't going to spend your training sessions focusing on running. This doesn't mean you can't run, but if you don't practice your pull ups several times a week (and I'm talking 5 times a week) you won't be doing 20 pull ups.
Likewise if you are concerned about your conditioning and endurance for your particular sport, you'll spend several days a week working on your conditioning in addition to training for your sport. You won't benefit by doing 1 rep max lifts if your focus is on your conditioning.
Once you start the training program for your goal there will be various different ways to perform the vast majority of movements. What is the best way to do a kettlebell snatch, the best push up variation, the best pull up variation? This all depends on your specific goals.
'The Best Way' is relative to what you are training for. Which is why there are so many ways to execute actions.