Aw man, I never liked this question cause my favorite is always changing.
Panel de Pon was a game pretty close to me, and I loved that game a ton.
Animal Crossing New Leaf was also pretty awesome too. It helped me during a harder time in my life, and I deeply appreciate it for that.
But if I was to say the game I've played the most, and just have enjoyed for a long time? Probably Smash 4. It's the only game I've ever seriously played competitively, and even after almost 2 years of it's release, I still play it almost every day.