What are the core differences between strawberry varieties?
I can only answer this for northern europe:
In Europe 'Elsanta' is the variety most grown commercially. Its because it stands up to transportation better then anything else. But its taste is lacking. Given a choise, get something else, even if they look good, which they will.
Grown in Denmark:
Honeyoye - early. taste ok, not great.
Sonata - very good strawberry and its mid season.
Polka - good taste mid season.
Florence - late season. Good taste. 

My experience with strawberries is get it locally, always. The great tasting strawberry varieties don't stand up to transportation very well, Its best if they are eaten within hours after picking. If that is not possible I would get strawberries from as cold a climate as possible, because berries in general get more complex flavors if grown under cool condition.