You put the wrong question. how to store — no difference, the data will not deteriorate. The question is what are you going to do with them. And here are the options:
If you want to make sample users by properties like group membership, such properties should be explicitly. To normalize or not — decide for yourself.
If options are used together, for example when you render the page for him and most of all, it makes sense to package the array into json/xml.
I personally like the version of Wordpress where there is a separate table for named options ( user, post, or whatever ) and to be stored in either a single value or an array in separate lines, but with the same name, on which you can make a sample or a serialized array as desired. Precisely how convenient is to use them. And, if desired, all options can be mixed.