Hi,
Which color is the best?
Which music is the best?
Which isolator is the best?
Generally asking for "the best" is useless unless you give informations in which regard.
In my applications I always have chosen the best isolator: In one application it was "optical" in another it was "magnetic", in another it was "capacitive".
Even worse: I used more then 10 "best" but different types of optocouplers.....
Each isolator comes with a datasheet.
Each datasheet has a lot of specifications.
Go through them item by item and decide if this is important for you and where you set the limit.
And there are other things - maybe important for you:
* price
* availability
* already in stock
* good reputation
* ...
Klaus