moTi - 1:12 pm on Feb 3, 2013 (gmt 0)
I always opt for something that fits full screen so the visitor doesn't end up enlarging, scrolling, etc.
you don't need "responsive design" for that. for example, fixed layouts will be autoresized upon loading with this code:
<meta name="viewport" content="width=1024">
works for landscape and portrait mode.
300x250 and they do better on the mobile site than on the desktop
maybe because they fill a good half of the screen? ;) i wonder why no one is using the recommended and dedicated mobile banner 320x50? it fits best for mobile devices.