Honestly, I never expected to play D&D again, much less fall in love with it again, so I could give a nod to Dungeons & Dragons 5th Edition.
I could also mention Wu Xing, which combined some of my least favorite things in a deliciously over the top, playable package.
Ultimately, I probably have to go with Marvel SAGA. Having ran Dragonlance SAGA, I thought it sounded neat...I didn't know it would become my favorite superhero RPG in existence (and still is to this day!).