It doesn't exactly work like that, when you add third-party providers you are including their catalog of games. And obviously popularity is built on the trust foundation, if a provider wasn't reliable we would not see them getting that popular. Of course, when it comes to issues or problems, we will take full responsibility where it is due.
That's true, just because one place is popular doesn't mean that it is the best one, think about it this way, there are two games, one of them is listed in 1 website that built it and that's it, there is another game and it is listed in 5000 different websites that provider sold to, which one will be played more? The one that was sold more, that is about marketing of the person that created the game and not about how great it is.
This is why I do not agree that the most popular one is the best one, and even providers are like that, the one that does marketing amazingly doesn't mean that they are the best one, I would say you should test them all, popular AND unpopular ones, and you will see that some of the less popular ones could be awesome and just not marketed well enough. This is of course not common like most of the time, it is just a fair warning, because it would be something that might help you, otherwise you could ignore this and 80% chance you will still pick the best one by picking the most popular one.