My favourite player is Wawrinka without question now. When I was a young kid, I liked Rafa a lot, and kid me was definitely a Rafatard, however I found myself gravitating towards Roger more and more as I got older. But when Wawrinka burst onto the scene in 2014, he instantly became my #1 favourite. I barely miss his matches. I liked him before he became a top player, it's just that he wasted some of his peak years because of injuries and unsatisfactory commitment to tennis.
I also really like Them, he is my #2 fave currently, I remember watching him against Rafa in Buenos Aires for the first time in 2016, and I was wondering why the hell is this journeyman with a cap pushing Nadal so hard on clay, ridiculous, Nadal was actually playing well. I knew at that moment that Thiem was a serious player. We will see how far he runs with it, he doesn't mug around anymore.
After those 2, it's Roger and Rafa, and for a top 5 list, I'd say we toss Dimitrov in there. But he has disappointed me so many times, I watch his matches for the sheer entertainment value of how much someone can choke.
Federer will always be my favorite. He is the reason I even watch and play tennis. But Thiem has been my solid #2 for several years now. I love them both so much; their game, their personality, etc. And I'd say that Wawrinka would be my 3rd fave over the years. I absolutely love each of his Grand Slam Final wins.