I primarily wear actual children's/baby diapers due to cost and actually being able to buy in a store, but there are a few I haven't been all that impressed with.
First are Ninjamas. The first batch at least was way too small and the L/XL had a tendency to rip easily while even L Goodnites go up just like my regular panties. Regardless, this has scared me from trying them since.
Second, the only adult diaper I have ever tried, Equate women's pull ups, had a tendency to leak immediately if I was wearing them absolutely perfect. I got the S/M size, but they still felt too big. Plus I don't like how they make me feel like an old person.
Lastly, the updated Kroger Comforts size 7 baby diapers. The old ones were my favorite tape style diaper because they were so cute and soft and fit me surprisingly decent for a baby diaper since the sides were decently stretchy, along with coming in a smaller pack for discreetness. However, awhile back, they redesigned them and I believe changed suppliers, so now they no longer fit me without rigging up some extensions from torn off sides of other diapers. Since then, to get my tape style diaper fix, I have had to resort to the Dollar General equivalent, which I don't think is as cute or soft, but the sides are still thankfully stretchy. It's just Dollar General has always been inconsistent about keeping these in stock.
I would also mention Pampers Easy Ups 4T-5T as they didn't fit me having a similar problem to Ninjamas, but I have not tried the 5T-6T yet since those came out, so I cannot judge them fairly.
If I had to mention one that I was mad at the most, it would probably have to be the Kroger Comforts because they messed up such a good product. I've even seen actual parents complain in reviews online saying they aren't as good as the old ones. The only thing I found interesting is they did change them to the absorbent 3 channel thing, similar to Pampers, although for my purposes I think I prefer the more basic single channel thing of a traditional diaper.