i'll compare what diapers/pull-ups i've tried to xl goodnites as sort of a basis, starting with the goodnites.
the 140+lb sizing is meant for a 140lb sphere, i'm 5'8", 36" hips 32" waist and weigh ~140 and they fit snugly due to the elastic but have probably an extra 4" of stretch on either side. the internal lining was extremely soft and comfortable, wicked piss away pretty well and the SAP is of a pleasant consistency. there isn't too much padding in them, and they can hold ~1 wetting easily, and have pretty tall leak guards and conform to my body well. once wet though, the SAP will definitely move around. they'll just stretch over an erection, unless you're big enough that they already barely fit.
the baby diapers i was able to wear in highschool (~15/16y.o. then, mid 20's now) were all similar in texture and capacity to the goodnites, and the features on their product pages like the 3-core layer thing are actually pretty nice, kept the SAP in place but were still comfortable and pleasantly squishy and wicked water in and absorbed pretty quickly, etc. sadly they were really at their limit even when i was 16, so unless they make size 10 with a weight rating of something like 80LB adults are either never going to fit in them, or they'll just fall off the second you try to move. pampers easy ups were really interesting, but the 4t-5t ones i tried did not have enough stretch to get over my hips.
the only actual adult diapers i've tried thus far have been betterdry/crinklz. i bought them while horny so i got a 4-package case, which came in a large, relatively plain white box which would be completely inconspicuous except for a large M in a cloud logo, and the box was flimsy enough that someone poked a large hole in the side when they picked it up, which gave me a moderate heart attack and left me paranoid for ~1 month that someone'd seen them, so be wary of that. the plastic backing is somewhat nice, slightly textured and not excessively loud. the main pad's surface in the middle is a little bit rougher than the goodnites/baby diapers, but not irritating. it took me a while to realize i had to tuck the leak guards in because i'm retarded but after that they probably won't leak unless you really try to test their capacity. the SAP is really pleasant, and the cotton/fibrous binder is also pretty soft. if you really soak them (2-3 full bladders) they'll start to sag a bit, and if you walk around or stretch and etc. the plastic will stretch out a little, but the weird double tape system mans you can lay down and readjust to get them snug again. i've had 2-4 out of ~50 so far where i really had to be careful when putting the tapes on, however once they are on they hold well. a snap-crotch onesie is pretty nice to hold them up snug imo. next to no space for an erection with penis pointed down, can get kinda half-chub. i personally avoid pointing mine upwards because i'm worried about leaks, but with it upwards there's plenty of space and depending on how you tape it up enough SAP to feel nice.