Massive will always be the "go to" synth for when I'm writing music, and I'm sure that's the case for a lot of people. It's pretty simplistic and you can achieve a ton with it. I guess a good way to put it is, since that was really the first plugin I started using, it's just grown so much on me that it's a natural default for when I'm adding a certain sound I need. Tbh, I am getting a bit tired of it though, I need to put in some effort and get familiar with more synths.