This is ignoring boosts, this is natural coin gain. Yes you always gain 1000 or 500 but the modes have different gains. These are all based on solo play.

Conquest is probably the slowest as most games go on for quite awhile, I have never actually timed one but it seems like they go on the longest.

Plunderball is a close second but also not due to the fact that if you can get the ball quick enough the game can be over in a little over a minute, maybe less if the enemy team is more focused on your teammates and killing not your ball.

Annihilation forces you into a 5 minute game that has no variables.

So what we have here is Annihilation > Plunderball > Conquest.

Anyone have anything to add maybe change?