Normally, I'd say Quick または Puckleberry fanfictions (although I 愛 some Finchel ones) but lately people have been coming out with some really impressive Sam/Kurt stories.
I'm a die hard Quick fan, so any of the Quick stories I find amazing! But I also find some amazing Brittana stories, which are usually hilarious and different, but very creative in my opinion. And then あなた read some totally ランダム never gonna happen ones such as Puck/Kurt, Quinn/Artie または something like Mercedes/Artie, which would never happen, but is fun to read!