Warhammer Age of Sigmar: Storm Ground

Units are unlocked in automatch via increasing your faction level. This popped for me at faction level 20.

The fastest way I found to earn xp was having your opponent quit at the start of the game. This nets you 750xp. Any time I actually played the objective I would only get around 650xp. This makes me think how much xp you get is tied to how quickly you win the match.

Using the quitting method I reached faction level 20 after winning 33 matches.

Note: The person quitting will get no xp. I was boosting this solo so it didn't matter to me. If you are boosting with another player, then playing the match properly and letting someone complete the objective will give both players xp (with the loser getting around 300xp less). However, this game is super slow to play, so I think the quitting method and just switching wins will still be faster for you.