2008 1st gen air OS question.

[elf69]

At present my 1st gen air is running El Capitan which is newest supported but it runs poorly.

I'm going to sell the air on local sites not ebay.

Should I leave as El Cap or install 10.7?
10.7 ran smoother than el cap.

but would newer os make it more saleable?

seen these go for over £200 locally.
So plan on selling for little under that in hope of actually selling it.

It is in fair condition considering age and previous owner had new screen fitted.

 

[dear.leader]

Probably best to leave El Capitan installed for resale purposes. It should run alright anyway, at least initially when the installation is fresh and before the new owner's installed a bunch of programs that start up at boot time.

You could also make some modifications to the OS before handing it off to the new owner, like disabling the Finder transparency effect, which is generally good practice on older devices.
http://osxdaily.com/2016/01/02/disable-transparency-effects-mac-os-x/