I have *shockingly* collected a number of official Apple Watch bands... I’ll just share my opinions on comfort based on what I have (in the order of most to least comfortable):
Woven nylon > fluroelastomer sports band > leather loop / Milanese loop > classic buckle > link bracelet
Woven nylon (which I guess extends to the new sports loops) is by far the most comfy because it is light, very breathable and isn’t damaged by water or sweat. Unlike the flouroelastomer sports bands that are completely waterproof, woven nylon can be slightly uncomfortable if completely drenched until it dries. But overall, I prefer the nylon’s breathability over the fluroelastomer bands.
The fluroelastomer sports bands feel a little stiffer and are not as breathable (the Nike ones are obviously better in this regard) as the woven nylon but still very comfortable.
I ranked the Milanese loop and leather loop together because it is difficult to determine which feels more comfortable. Milanese loop can pull on hair and fabric but it has excellent breathability and it is unaffected by water or sweat (yes Apple doesn’t recommend it for swimming but that’s another discussion). On the other hand, I found the leather loop more comfortable on cool days but a bad option for a hot day since it is not as breathable, and sweat (and water) isn’t good for leather.
Side note: The leather loop is my least favorite of the bands because it does not feel like leather (more like plastic) and thus, I returned the only one I bought to Apple within two weeks. This isn’t an issue for comfort, its just that it doesn’t “feel” and “look” premium enough for its price, especially relative to the other “premium” options.
Classic buckle, like any leather band, is comfortable on cool days. Not suitable for work outs, hot days or even rainy days. In terms of comfort, classic buckles can’t beat the Milanese or leather loop since those are “infinitely” adjustable, something to consider since the wrist size can change slightly during the day.
Note: The classic buckles are actually my favorite bands because of the look and the colour options. The current generation of classic buckles are all more comfortable than the earlier generations (those were stiffer).
Finally, the link bracelet is hands down, the least comfortable one. I love the look very much, but comfort is an issue. Yes, the links are easy to change, but this is not what you want to do during the day when your wrist size changes. It’s not as breathable and it can get quite uncomfortable when you sweat. I don’t wear the link bracelet very often as a result.
Hope that helps.
I'd say this is solid and spot on advise based on my limited experiences. I rotate through the woven nylon with buckle, fluroelastomer and a milanese loop knockoff by Spigen and find them all to be comfortable and suitable for different reasons. Eventually, I'd like to try one of the new sport loops, I keep hearing great things about the comfort of them. I'm not wild about the subtle technicolor nylon embedded in them though. Hopefully they find a way to tone it down a bit. Sooner or later, I'll end up with one.