If you want tokens and don’t care about other drops, breeding is the best time.
There are other times when both legendary and epic tokens drop, but the percentages are higher in breeding… You just get more “junk” imo.
But if you are attending to maximize game progression, then even the other good stuff doesn’t matter, only timers and tokens.
So, breeding and feeding are the best when you look at it that way.
Hard advice to flow though since it means you will do less well in the season. It if you are not in Harbinger (or at least obsidian, until 65s come out), doing “well” in a season means less total progress in the game.
That is a very technical way to think about it.
You should do what makes the game fun for you.
Edit: sigils vary the least between events, but they drop at slightly higher percentages in fortification, breeding, and feeding. I think the lowest. Have seen is 14% and the highest is in feeding (and sometimes fort) at 18%…historically… All subject to change in the future.