Operator comparison will create one more string object, which is to be deleted very soon and that makes it generation 0 on the heap. Microsoft claims garbage collector is blazingly fast on gen0 for .NET Framework, but I don’t know the situation for Mono.
As a veteran software developer I would recommend ignoring such micro optimizations unless it is called more than a hundred times per frame. I think such optimizations are in the category of compiler optimizations.
Now time for shameless marketing 
Code Enchanter automatically converts all of your tag operator comparisons to method comparisons from your source code.
For example myObject.tag == “myTag” to myObject.CompareTag(“myTag”)
It has some other performance tricks as well, it’s available on Code Enchanter | Utilities Tools | Unity Asset Store