I would go with tall. I see no reason to go with a wide format although I am no database expert. Only thing I may add is a "group" id. while you may have only one group now in the future you may need the ability to sort on multiple groups where the same user has multiple groups assigned to them. you could always change later but if you add a group id column now you dont have to worry about that in the future.
6000 rows is nothing for a database table. I think you will have a big complicated mess if you try and do this with a wide table. IMO of course. If you are worried about saving space which isnt a concern imo you could serialize the dataset and store everything in 1 row