Never Can Say Goodbye is great. She also does a duet with the character Puck of Just Give Me A Reason which is great too. I love I feel pretty/Unpretty too.
Love this. As other stated below Never Can Say Goodbye is a good Quinn solo :) Also would love for you to check out Glee - Wide Awake or Glee- Shake it Out
it's not just her voice maturing but i do believe dianna (who plays quinn) couldn't breath correctly before and got it fixed (around season 3 maybe??) and then realized her natural range is a bit lower or something similar i forgot the details because it's been a hot minute but yeah