I had a 2011 13" MBA and switched to an 11" MBA in 2013. I greatly prefer the 11" MBA, but that is primarily for the size. So light and portable, it's terrific to have so much power in such a small package (I have the i7/8gb/512gb model).
The extra pixels on the 13" screen are nice, but I don't mind the 11" screen - seems like a reasonable trade-off for the benefit of the small size. Things are definitely smaller due to the higher dot pitch however. Very noticeable when I first made the switch. I ended up setting larger default font sizes in several programs. Apple Mail was especially an issue, the default size font was fine on the 13" but just too small on the 11".
I like the 16:9 aspect ratio of the 11" screen - perfect for watching movies. You do need to scroll more when web browsing though. But my MBA spends most of its life at home, connected to a big external screen so the smaller built-in screen doesn't matter there.
In the end, it all very personal and subjective. You should go to a store and play around with both if possible, that's what I did. There are many, many threads on this topic if you browse back through this forum too.