Write Your Name and Stars Dance are the only VIABLE single choices this era.
Undercover has extremely cheesy childish lyrics, "you're a sexy machine, you're a hollywood dream, and you got me feeling like a homecoming queen!"
In Birthday, they will probably remove the moans like in the tour version of the song. Which will take a lot form the sing catchiness.
Save the Day is just too similar to Slow Down, similar songs tend to flop.
Love Wll Remember is just not good as a single, it's not even a good album track. I personally like it but critics/GP is not having it with this song.
Stars Dance and Write Your Name have this sensual, dreamy and mysterious feel to it. They're so unique. Selena doesn't have a strong voice BUT her voice absolutely works with this sexy enigmatic sound. These two aongs are iconic form SD. LYLALS is a perfect demonstration of what I'm saying.
Tl;dr version: Stars Dance and Write Your Name are the best single choices from SD.