Difference between FIND_IN_SET and LIKE
I would use LIKE for one very good reason. From the documentation here - "This function (FIND_IN_SET) does not work properly if the first argument contains a comma (“,”) character".

You could always use an EXPLAIN  to check on performance - but simply for the reason above, I would not use it.

[EDIT]

You could always use LOCATE(). I strongly recommend that you don't use MySQL's SET datatype. It's non-standard and illogical to say the least.