Let me start out saying that ANY loot system is potentially the BEST for you, and depends on your weaknesses and strengths.
Let me explain.
GDKP: is great for people who have economic literacy, like to earn and save gold through either farming or trading, or both. This system allows you to get BIS quicker than almost any other system. It is tied with loot council, but quite easily more moral. This system is also great for full geared players just looking for their share of the gold pot at the end! Do not show up to one of these unless you are willing to accept the math. If youre poor you will leave a little richer, but without an item. If you want to get better at this system, then read books by Charlie Munger and Warren Buffet.
LOOT COUNCIL: Is great if you are the type of person that loves to grift people. If your specialty is manipulation, then this is BY FAR the best means of gearing up the quickest, as it takes less effort and time than farming gold… Convince 39 players that they are being prioritized for loot based on some well sounding logic, and watch them earn you loot. You can bribe members of the guild which dont compete with your loot type to help perpetuate the scam. We call them the LOOT COUNCIL. If a system can be abused, then humans will abuse it. And there is nothing wrong with that! Do not participate in these unless you are at the top of the pyramid scheme. If you want to get better at this system, then read books by Donald Trump, or “influence, the art of persuasion” by Robert B. Caldini.
FREE ROLL: This system is THE BEST SYSTEM for people who are not economically literate and are not great in the art of manipulation. It is best for someone who has very few or no BIS items yet, as you get a chance to roll on absolutely anything you may need. If you already have most of your BIS, then you are wasting time here. Move onto a SR raid, where you can be one of the few people to roll on the only item you need. There is no getting better at this system other than realizing when its time to move on. This is probably the best system for the majority of people.
SOFT RESERVE: Best for people who only need 1-3 items. You can leave these groups before they start if theres too many people rolling on your items, but chances are, you have a lot of people reserving garbage that should really be in a Free roll run. This is also on par situationally being the best system for the majority of people.
DKP: best for the people who are very reliable in life, and show up to every raid, but do not have the time to farm gold or manipulate people to funnel them loot. This is the BEST GUILD SYSTEM hands down.
So to conclude, it is not a matter of BEST or WORST in general. It is very specific to you, and you should personalize your experience based on your strengths and weaknesses.
A lot of people, through ignorance will participate in runs which are sub-optimal to their strengths and weaknesses then complain afterward.
Ignorance is a key driver in human misery and this post is an attempt to help people find their place in the world.