My apologies on this list...It is a little too late for corrections so I just hope I didn't mess too many people up...

The highest percentage of Iron Chest Pets are:

Halloween Guinea Pig  70%          Grim Eagle Owl    60%

Gold Bearing Turtle       60%           Garden Bunny     60%

Bat, Chimney Sweep, Flirty Hippo, Treasured Phoenix,

Voracious Lemur, & Wise Raven   all at 50%                                    

And the Pensive Spider ---- 60%

Good=natured Hedgehog ==== 70%

Got mine with those two so beyond those ---- ????

BUT, the previous post is for SILVER, not iron!!, so those are all incorrect.

Crap, I got an iron chest from feeding a pet and it did not register in the tally. Shut down my iOS game and restarted. I subsequently got two more iron chests and they still did not register either. Grrr.  Will wait for a bit before wasting food on feeding my pets.

Update 1: I used the list of “best Chance pets” above, such as Grim Eagle Owl, which only has two chest options, one gold and the other (supposedly) iron. I got the iron one, but it was not counted. 

Update 2: just saw someone comment that original post listed SILVER chest pets - explains my “issue”. Back to using actual iron chest pets  got my iron chests right away with these two pets:

Pensive Spider — 60%

Good-natured Hedgehog — 70%

Are you sure they were iron chests? The wooden and iron chests look very much alike. 

I got Silver thinking it was Iron.  LOL!  Took me awhile to figure it out. LOL!  Good Luck! 

I used the list of “best Chance pets” above, such as Grim Eagle Owl, which only has two chest options, one gold and the other (supposedly) iron. I got the iron one, but it was not counted. 
 

Update: just saw someone comment that original post listed SILVER chest pets - explains my “issue”. Back to using actual iron chest pets  got my iron chests right away with these two pets:

Pensive Spider — 60%

Good-natured Hedgehog — 70%

The halloween guinea Pig is 70% for a SILVER chest. it doesn't have a iron chest. silver or gold.

Same with the Grim Owl.

Turtle is 20% for iron.

Garden bunny is 60% for SILVER

This is on my iPhone game (level 53) not playing the CC on that game.

Is my game messed up and not showing the right % of the pets?

I'm confused

Of course I would get gold from good-natured hedgehog.

so..iron from pensive spider and emerald dragon

TLB2, I'm seeing the same as you -

Halloween guinea pig - 70% silver; 30% gold

Grim eagle owl - 60% silver; 40% gold

Gold bearing turtle - 20% iron; 60% silver; 20% gold

Garden bunny - 60% silver; 40% gold

ETA: I went back and looked at the ones listed as 50% and those are wrong also.

Bat - iron 35%

Chimney Sweep - no iron

Flirty Hippo - iron 40%

Treasured Phoenix - iron 25%

Voracious Lemur - iron 35

Wise Raven - no iron

Just copied this from the old BF forum. Hope it helps.