If you are reading this, then there's a great chance you created an account here. If not, then I would highly recommend you do so, so that you may bring your interaction to a whole new level here in the forums.
While I saw playing around customizing my profile and profile page. I immediately noticed that I could include my own profile banner.
and trails, and countless uploads (okay maybe around 9-10). I came to conclusion that the best aspect ratio and resolution for a profile banner was:
Aspect ratio: 4 x 1
Resolution 1100 x 275
If someone finds better numbers, then I more than encourage you to share. After all, that's the great part of the forums!