I love how easy t13 is to get. All the bosses that drop tier are before spine so you can skip that shit show (unless you want/need weapons), and at ilvl 700 (or close) from invasion gear, you will absolutely wreck heroic 25m solo. Dragonsoul is also a short raid so you can do it quite fast.
Same for heroic Firelands if youre into those (I actually went back to t13 on my hunter whem I got the hc version, that set grew on me in ways I never imagined, its super detailed and I love the helm), and that one has 2 mounts that can drop (well technically so does Dragonsoul if you dont skip spine/madness).
T11 stuff is a bit more annoying to farm because its 2 seperate raids obviously. And im not a big fan of t11 as a whole.
I got bored so I did this:
Please note this is just my opinion. That being said, T8 = GOAT
While I agree with T8 being the GOAT overall if you exclude T17 Mythic, you choices for some sets are... questionable for me :3
Of course a lot of the sets vary by race aswell so its all relative.