I'd definitely need to see some rules for the fight. We just dropping 2 Wizards in an arena? Can they buff up, summon things first as long as it's within their daily allotment of spells? If we are just dropping two wizards into a ring and rolling initiative, then I'd have to go with Abjurer. They can counterspell all day with a 3rd level spell and have a reasonable chance of working even on 9th level spells.
But if they can prep a bit before hand then I'd probably have to go with a Necromancer. At 20th, using all 3rd-9th slots they can summon 128 Skeletons that will be 33hp each, with a melee and ranged attk of +4 to hit that does 1d6+8 damage each. I'd probably save the 8th and 9th slot for something else, like Foresight actually, but even then they still have 98 minions. Actually I'd probably keep that reserved for a 9th Lvl counterspell to the inevitable Meteor Swarm which could eat up that army. Also if he gets to use his Arcane Recovery before the fight he gets another 10 spell levels back, which I'd also likely bank for some non Animate Dead spells.
Either way that army can do some serious damage. Of course the other wizard might just fly away, or whatnot, depending on the rules of the duel there are some ways to counter that, mostly by avoiding. But barring that, the auto advantage on Saves and Resistance to spell damage the Abjurer gets puts them way ahead of other casters in a magic duel.
But if they can prep a bit before hand then I'd probably have to go with a Necromancer. At 20th, using all 3rd-9th slots they can summon 128 Skeletons that will be 33hp each, with a melee and ranged attk of +4 to hit that does 1d6+8 damage each. I'd probably save the 8th and 9th slot for something else, like Foresight actually, but even then they still have 98 minions. Actually I'd probably keep that reserved for a 9th Lvl counterspell to the inevitable Meteor Swarm which could eat up that army. Also if he gets to use his Arcane Recovery before the fight he gets another 10 spell levels back, which I'd also likely bank for some non Animate Dead spells.
Either way that army can do some serious damage. Of course the other wizard might just fly away, or whatnot, depending on the rules of the duel there are some ways to counter that, mostly by avoiding. But barring that, the auto advantage on Saves and Resistance to spell damage the Abjurer gets puts them way ahead of other casters in a magic duel.