Level 20 is what most of us use.  

Good luck.  

Going for 20 may just be better anyway for the extra silver/potential gear. I just wanted to make sure I am concerving as much energy as possible for this current fusion. Thanks for the advice.

L3 will still give you more Dungeon Diver points/energy, but L20 delivers more XP for leveling toons as well as a chance at usable gear and more silver.   

note: stage 3 gives more points/energy for *GEAR HUNTER* (formerly dungeon diver) but not for the dungeon tournament itself

And even for gear hunter, the points/energy for stage 3 is just fractionally better, but the silver & xp are far far worse. The main advantage of doing stage 3 for gear hunter is it's typically much much less time consuming than stage 20

IIRC that only applies to the event dungeon too since it doesnt drop brews / shards.  Either way I always run 20s with food.  Cant imagine the efficiency loss is notable. 

Someone did a spreadsheet years ago, but not counting event dungeon I think it's still accurate:

Stage 3 of a dungeon gives 0.8 points/energy for gear hunter and 0.38 points/energy for dungeon tournament

Stage 20 of a dungeon gives 0.76 points/energy for gear hunter and 1.11 points/energy for dungeon tournament

It doesn't have stats for hard 6/10 for dungeons, but unless you're farming for mythical gear the points are still better for normal 20. Though hard 10 is much better cvc points

The time to farm a stage 3 is if you dont care about xp or silver, but want to get dungeon divers done faster. Picture doing 500 runs on stage 3 at 10 seconds each or on stage 20 at 3 minutes each.

(of course, a lot of end-game players are at the point where they 1-shot waves anyway, so the time factor is basically moot for them)

That is what I thought as well, but I was proven wrong by the data in the RSL-X tool. 

That said, I still run L20 to max out the gear/silver/XP.  I value that more than a bit more energy efficiency for DD points.      

Which part is wrong? That data goes way back to before I even started playing, so I'm not surprised if something's changed, just curious what's out of date now

I jumped the gun doing IG today.  I should have waited for cvc, especially if it will be personal rewards.  

I thought I was responding to Short, but apparently I didn't hit the reply button. I originally thought that L3 was only better for Event Dungeon, but someone on Discord corrected me, but for my play-style, L20 is still better.  However, I always run H10 for Dragon when Speed Gear is boosted.  Marius solos it, so I can still run 4 foodies.   

Assuming RSL-X has correct data, you can actually view all the efficiency information for all event types by each Dungeon type (and even campaign): Gear Hunter, Tourney, Path, DoF:

https://rsl-x.gg/

Tools/Efficiency Lab

I am gonna run the entire Event Dungeon Tourney tomorrow to max out CVC Pts. 

Yeah im the same.  Stage 20s thru and thru, especially during fusions.