If travel weight is the primary concern get the 11. It is tiny.

I have had both. Now I have the 13 and want the 11. The change in carry weight from a 15 to either MBA is life-altering.

The screen on the 13 does give more acreage to work with. I got the 13 primarily to get a bigger SSD.

With the 11 you will want to live in one window only. The screen size is optimized for portability rather than productivity. On a plane the 11 is a gloriously useful size.

I dock my 13 to a Thunderbolt Display at work.