It's so hard to talk about just one without talking about all of your favourites! Personaly, I'm obsessed with SuFin and PruCan right now. I was a fan of Franada for about a week at the begining of my joining the fandom, but now it kinda creeps me out. ^^" No offense to anyone who likes it! One of my now-favourite fics actually got me hooked on PruCan~
I also love UsUk, Spamano, Giripan, RoChu, GerIta, EgyptxTurkey (does it have a name?), EstoniaxLatvia, SwitzAus, DenNor, HKIce... See, hard not to express all the pairings that you ship. OTL