I like to get as many as I can of course and me and my group often make it a bit of a competition to see who can get the most on the community day! Though I’ll always keep at least 1 of each of the evolution line and am (and will be more with higher friendship levels) now using my excess shines for trades to either get other shines, be nice to friends who missed the day or most importantly for regionals.
One for each evolution is enough unless the are useful for battle like Tyranitar, Dragonite, Kyogre, Gyrados then it is more about high IV for those to actually be useful.