My favourite portal: Circular Transmutation
This portal is special to me in three ways. First of all, it is a symbol for the most epic Ingress weekend I've ever had, during Epiphany Night at Schloss Kaltenberg. Second, it's our team's portal. I did all the technical stuff of connecting the bike pump game with the portal in-game. Third, I got my platinum explorer on this portal :D
It's also the only portal, apart from NL-1331, of which I always keep a key in my lockers.
(I don't use social media :P )