I actually take a different approach. Yes Eggs are key in this game and therefore during breeding is good when you look at egg per gold chest. BUT I gave up on that idea. I only open them during Conquer The World.
I find that event gives minimal useless items (like fire and ice shards) and gives decent Energy and IF drops while still rewarding Eggs and Timers, albeit not as many eggs as during breeding particularly because you don’t get mystic frags. But doing well in PVP events i find offsets getting less eggs directly from the chests themselves.
Consider this; if you are desperate for Eggs, speeding egg missions when you have the token boost is the most efficient way of getting more eggs. From 27K gems (1 large pack) you are lucky to get 20K eggs, typically you get between 60-75% back in eggs vs gems used when opening gold chests. Sure you get other stuff too but most of that is useless compared to the value of egg tokens. Whereas speeding egg missions (the first 2) you will get 240 eggs for 120 gems (200% back).
Therefore opening chests during an energy and IF event will allow you to get a few extra tiers, and using the extra gems from those tiers to speed egg missions will likely payout more in terms of eggs received than if you opened them during a breeding event. Plus who doesn’t need Energy and IF?
Using this technique is often how lower level people (still in their 200’s, some low 200’s) are able to still have top tier dragons like Noc. They Speed egg missions with their gems,