I have a lenovo thinkpad yoga 260, but as I know these have a huge motherboard defect, so i plan to sell mine. I looked arround the internet and saw that i could buy: thinkpad x240, t440, t440s, t450, t460 or macbook air 2012, 2013, 2014. I had thin and light laptops for couple of years now, and thinkpad t, x series aren't that thin. I'm a huge thinkpad fan, but I like macbooks too.
Witch one do you recommend and why?
Those thinkpads are relatively bulky. I've used the T460. If you want lightweight the MacBook Air is the wait to go.
I don't know what your budget is. You may want to consider a 2014/15 MacBook Pro 13 of eBay. They're pretty light too. But they have a vastly superior screen and faster CPU. Compared to the Air. I went with the 2015 recently after comparing to the very same used laptops.