If I could experience all of my favorite games again, I'd probably pick all of them! But if I had to choose only one, it'd be TF2. I started playing it regularly around 2017 and after two years and 1,500 hours (absolute rookie numbers for this game) I'm starting to feel the burn out.
Even with really long breaks from late 2020 up until right now I can't bring myself to boot it up. However I did play a lot of new games like Apex Legends and they were fun because, well, I played them for fun! I felt like I could see myself improving over a few months, which I never had with TF2 because most of the technical stuff I learned along the way.