Serena - I think of Serena Williams, but I also think of someone quite popular and sporty, quite bubbly and fun-loving.
Selena - I think of a quiet, studious girl who's also quite creative - art, music, writing maybe. Selena Gomez briefly crosses my mind but not as much as Serena Williams does above. No idea who the singer is people are referring to.
Seraphina - I think of quite a posh, preppy girl with this name, someone who's quite well-off, quite popular, maybe a sports team captain or maybe completely into make-up, hair etc.
Sabrina - I do think of Sabrina the Teenage Witch. Of all your names, I've only ever met a Sabrina, and she was quite stuck-up and we didn't really get along, so I don't have a good association with the name.
Serena: Serena Williams and the character Serena van der Woodsen from Gossip Girl.
Selena: Associated with Latino celebs for me. The late singer and Selena Gomez. Has a sleek sound.
Seraphina: I think of angels and the Garner-Afflecks' daughter; frilly and feminine but not insubstantial or princessy.
Sabrina: ...the Teenage Witch, lol. If you evaluate it objectively, though, and remove the pop culture association it's a really nice name.