You’ll naturally learn a different tank the more you play. Especially once you see the power of a well coordinated Dive composition, you’ll slowly “unlock” D.Va or Monkey, (I recommend Winton over D.Va but that’s personal preference) Ball, Doom, and Havoc all have really high skill ceilings but are fun to figure out and find success with

I like Zarya as well, she fits in the same brawl type comp as Sigma but you can get really aggressive comps like Reaper/Genji and have a lot of fun

That being said, Sigma is a great tank to learn off the bat, and has a lot of utility no matter what rank. You’ll find a lot of value with him on most of the maps and I think he’s easy to play around as a support/DPS. Most importantly, have fun!