If the Inquisitor would be a warrior/rouge- Geralt by the book
If the Inqusitor would be a mage- Inquisitor by the book/DA world
In the books Geralt almost always looses to mages (once he killed one but from behind while he was distracted) or is easy taken down by their CC spells. Witchers are immune to charms and can sense magic (so they can predict spells being casted). However powerful charms (like Yennefer did to him in "Ostanie Życzenie" book) would easy take control of him.
Geralt has superior reflex, strength, speed, stamina, regeneration (but not Wolverine
) and combat abilities (plus he is really talented with swords) but his "magic" for true wizards is just joke (what Triss and Yennefer said many times in books). Their magic is enchanced in gamesto be usefull, but in books is weak and used only for small support in combat. Besides Geralt almost never use them.
He is able to dodge arrows and deflect them in air, but he would not dodge lightning or bear with being immolated.
However in books mages need time to cast spells, so taking in account Geralts speed- it be possible to him to kill wizard first. Normal human would not. In Dragon Age world however where casting spells is just waving hand or staff and BUM!- Geralt would be smashed. Judging by books of course... In games? Depends on HP, gear, STATS, stuns and stealth/guard mechanics
.
Source: I am from Poland, read all books like 7 times ^^.