which is best browser for osx el capitan 10.11.6

Frank,

The best browser is whatever works best for you.

I primarily use Safari, but I also have Firefox, and Chrome installed on my Mac. If a website is not compatible with Safari, in order, I next try Firefox, and then Chrome.

As Fred II mentoned,

best browser for you is that one, which best suits you and which can solve your request. But if you are asking about best compatibility, then you know the answer. Best browser for Mac is Safari. It has great integration, many features and is designed and developed by Apple for best experience with macOS and your Apple device.

Safari

I like the built in Safari.

Does it not work for you?

Are you looking for some features that Safari does not offer?