This are the best covers of 2010 (youtube only), in my personal opinion. Also, I wanna do a special mention to Greyson Chance and his cover of paparazzi that has more than 36 million views.
Check out the channels of this talented artists:
Alex Goot
Christina Grimmie
Julia Sheer
Eppic
Tyler Ward
Kurt Schneider
Chloe Boleti
Alyssa Bernal
Sara Niemietz
Jake Coco