Firstly these are very valuable and veey rare items, so I wish you the best of luck in finding them (I am looking for them myself)!
To address your concern about some opening nights with stickers and some without, this is completely normal. There are 2 ways to obtain an Opening Night Playbill: either get one from the theater on or around opening night, or you can buy them directly from Playbill on their online store. If you buy from Playbill they will have the sticker, and if you get it from the theater they will not. As to which is more valuable, it completely depends on your preferences as a collector. I personally like the sticker better for displaying purposes.