Help me adding song to my videos

So some people wanted me to add sounds to the video. I made my first four videos with song for the HTML Tournament, but I'm unsure if they were a good choice. Here is the HTML tournament videos: https://www.youtube.com/playlist?list=PLpv1kwP6N7LV54vPPb91Ht-WFht01tS4L

Where can I get some good songs? or should I add English pokemon / yugioh's openings (as they encourages you to be the very best!)? or maybe no song at all. Thoughs?

Christmas carols please

Https://www.youtube.com/watch?v=P-uFZVsgwZc

I don't think it matters much, just be careful with copyright.

Great video , it was so intense to watch xd
watch out for copyright like mare said if you going to use some songs , otherwise use dubstep/house songs i think would go great with the vid

Anything classical goes well with atWar

First 2 videos are pain in the ass to listen to if you ask me too much harsh sounds I think, the other 2 are ok, but I still prefer my music choice https://www.youtube.com/watch?v=921JeI4L78o

Keep calm and
reload, mate

https://www.youtube.com/watch?v=UvBbZpDRRzA