I suppose there is one true statistic to this, but it is going to depend on your skill. I would do the following:
On this Steam Post, which I agree with, many players say to do the Shadow Raid. The thing is, you need 4 people that you can coordinate with (something public matches don't really allow).
You need a 4-person team, and it won't work with pubs. You have to know exactly what you are doing and where you are going, and everybody needs full ECM
I've never tried this tactic, but from the sounds of it and this video, you play on the hardest difficulty (Deathwish for console versions, or One Down if you can handle it), go loud, and have your ECMs at the ready. Kill anyone you run into, and place an ECM when needed to prevent the 1 minute remaining alarm. You'll earn around ~$13 million each time in about 5 minutes.
For Solo games here are some options:
Mallcrasher Overkill or Deathwish.
For this mission, you'll want a saw to be able to break into all the ATMs quickly. You'll need an ammo bag as well to replenish saw blades. You can cause the 50,000 dollars of damage pretty fast with a few well placed grenades to end the mission. There is also a jewelry store which you can loot for some more money.
Hoxton Breakout Overkill. This one gives a nice payout at the end, though it's not very fast as it is a 2 day job.
The Pro job version also grants more money, but obviously carries the risk of not being able to restart. I don't recommend doing this one on Deathwish or higher as it can be pretty difficult soloing.
The Diamond Store on Deathwish or One Down. You'll want to take a "Control Freak" route, and use ECMs. This can be pretty profitable and fast. You may be even able to stealth it fast if done carefully enough by controlling the crowds and taking out the Guards.