(you can help me decide one from a overall choice, or a handful I could try)
Heavy:
I usually play heavy for high health pool and damage. primarily using speed boosting stuff to go across longer distances, due to him being the slowest.
Medic: (yes I know who Mercy is)
I kinda love to heal my team, and just a "Thank You!" (voice line or voice chat) brightens my day. I also dabble in a little battle medic from time to time
Sniper:
I play sniper because one shotting some random guy from 9 gazillion hammer units away Makes dopamine go yes
Spy:
For a similar reason to sniper with the one shotting, but his stealth and actually fooling the enemy with disguises is fun to.