It would have to be the Dragonborn so long as you are talking Mid or End game levels.
By just after the middle section of the game the dragonborn can have armour that makes him all but invincible, I maxed out my blacksmithing and enchanting so I had dragon bone armour with stats WAY past anything sane (a cycle of potions and blacksmithing and enchanting equipment meant you could have several hundred percent bonus to the stats etc. when making and double enchanting the armour and weapons.) My companion was full daedric armour and either of us could stand in front of a dragon and punch it to death before we would die.
Linked with weapons as OP as the armour means the dragonborn has a massive damage reductions and dealt advantage. bow and crossbow would cancel out however the dragonborn can massively overcraft the bow to do way more damage so again it wins. the range of magic I'd say gives advantage to the dragonborn again. Adding in the Shouts (Go third level and call in a dragon or massive storm, disarm might not work so just blast them into a wall and off their feet so you can wail on them on the ground?)
So overall I have no idea how Geralt would compare, just outmatched by the system letting the dragonborn become basically an immortal who could kill dragons with one or two hits from a handaxe.
Early level might be a different story however, catch it before the dragonborn runs away with the highly abusable systems...