Okay I just spent like an hour listening to all the sample songs for the Opera Gx contest and in my humble completely honest opinion. I think almost everything single song in the selection above is amazing (Except F). To add to this even though I voted for C I really hope whomever is in charge of making the decision which song is used for the background music for Opera Gx, they also listen to all the people who commented below and add a feature where the user can switch and/or shuffle through the sample songs and change them to which they are feeling depending upon their mood.

Also overall out of the sample tracks in the vote list above my top 5 are:

1. Track C
2. Track H
3. Track B
4. Track G
5. Track J

With Honorable mentions being Track A, Track D (Especially, really good song), and Track I.