It's a bit late to be tagged in anything really since my list is kinda solid, also please stop commenting "this was from 2013". Most everything from 2013 is eligible, deal with it!
#19 - Chandelier - Sia
A great cover on AGT:
This is Sia's second appearance on my countdown, the first as the main artist. She also appeared at #5 in 2012 with David Guetta in Titanium.
Hint for #18: This was my favorite artist I listened to for the first time in 2014.