Ryden. I think that's like everybody's.
I've never written it, and I don't know if I ever will, but I go on mad binges reading Ryden fics every so often. When written well...
Klaine. Just Klaine.
I'm only just getting into reading and writing for this pairing, but I love it so much already (and I love it in canon obviously.)
Mulder/Scully. Classic pairing; if I gotta read/write romance or kink or anything inbetween in my X-Files fic it's that. Totally canon (even if they spend half the show trying to deny it.
)
The Doctor/ Rose- I prefer Who fic that doesn't deal with pairings and stuff all that much, but I do love this pairing especially if it's dealt with in a way that it was in Canon (like the whole unspoken elements to it, the subtleties, the heartbreaking elements
It's beautiful when done well.)
Also, I don't know if I'd call it an OTP yet, but I'm getting quickly addicted to writing Patrick Stump/Justin Pierre.
So far, it just works really well, and they are just so cute and amazing together. (I've not tried to find others, but I've never heard of it before so...I dunno maybe it's just me.)
There's probably more...
I'm a little bit of a shipper when I want to be.