I really have to recommend "Invisible Cities" to everyone. I have read "Cosmicomics" and "If On a Winters Night a Traveller" and it's still my favourite. Maybe it was the translations I read but I found "Invisible Cities" to have a far more flowing and beautiful style than the other two. The language in "Cosmicomics" seemed very simple and even stark to me in comparison.
Still I really enjoyed "Cosimicomics" I first read it quite quickly because I was borrowing it but I might have to pick it up and re-read it now.