2014 had Minecraft and Rogue Legacy, so that was a great year for me...
in 2015 I mostly played... Minecraft and Rogue Legacy, Ya know even after getting the platinum I have wanted to move onto other games, I've a back log of so many quality titles, not just Vita stuff but a ton of psp/psone games too. Ooooo this year we also had Super Time Force Ultra, that was amazing, with bonus ps characters from Journey, the order and Shuhei Yoshida himself as fighters. Great fun game.
I finally fully completed Liberty City Stories on the Vita a while ago, got that on launch of the PSP, but never quite got into it, the ability to map the second stick of the Vita to either the D-pad/ face buttons/L/R is just so fantastic for making some PSP games so much more playable than they were on the original hardware.
Since the Vita has come out not only have I bought a ton of the psp games which I "Arrrr matey'd" during the psp era but also I've kicked my psp-go into being a full emulation machine for older generations of consoles/handhelds and handed off the psp/psone work to the Vita almost completely (wish so much that the original Lumines/Lumines2 and Every Extend Extra came to the psn store for the Vita, guess it's a music licensing issue there tho)
All in all for me the best years of the Vita are all the ones since it came out, it pretty much put my 3ds to rest not too long after some of the big games started to come out for it, then it was also included in the psn+ monthly games so that got me far more interested in the Vita every month which pulled me from being a Nintendo handheld slave and From the 360 over to the ps3 a good deal since I was also getting free monthly games on that system from the subscription. A handheld seen as a failure by some has worked it's way to pulling my gaming euro's away from Sonys 2 rivals in the sector.
Should add here, I like games... a lot, here was a shot of just how much I loved the X360 during the previous gen to be drawn away by the lovely Vita, tis a good lil handheld.

Sorry for adding a large image which is off topic, but just wanted to make a point that I'm not someone who buys 1 game a year being swayed from a system haha.
Edit - Had to add that picture is a little out of date and has since been alphabetised for "fun" both X360 and my 177 Gamecube games.