I really like the song "Why", and TBH it's way better than both Jessica and Tiffanys main-songs (Though I prefer Jessicas album as a whole, I love almost every single song)
What I do found funny though is that their solos really shows who is actually a good performer and who is not. Unfortunately Jessica has not been able to perform on the music shows, but Taeyeon is just miles and miles and miles better than both Jessica and Tiffany when it comes to live performances.
This comeback stage DEF proves that she can do complicated choreography(that needs to be perfectly timed to match her dancers), sing really well(no choking out like Tiff) and still have that great stage presence.
I never liked Tae much, but she is an amazing performer and artist.