Isnt top chest the lowest value chest?

true , depends on how you see it , top chest is 1st chest , but also 4th chest i shouldve specified :P

Best chest from nm and unm are the only 2 with leggo book and sacred shard has possible rewards , so its better to secure one of them over trying for 2nd-3rd chest from both.

Edit: its lower than best chest from UNM but until you can get that , its better off getting that top NM chest since the rewards are similar to UNM top chest just lower % . otherwise you prevent yourself from getting extra leggo books and sacred shard that may or may not drop!

I think it depends on how RNG is set up.  If it is totally random on all reward we could get 3 potions.  Chances could be 1/15 x 4 for any reward.  

yes it is , but with lover chest you wont get the option to get a leggo book or sacred shard . Still down to rng overall but those wont be option in rewards unless its top NM or UNM chest :)

This isn't up for debate guys. The stats are all data mined:

https://imgur.io/a/ebytw5F

@kramaswamy.kr ..... Thanks.  This is a lot of good information to sift.    

LOl i hit UNM NM AND BRUTAL every day last box lol