As a third year owner of my web, and a new owner of the kestrel, I can tell you, they are very different tools. If I am forced to choose between the two - I'd quit hunting. Haha there isn't a right answer there, it truly depends on the person and their hunting needs and preferences.
However, I will give you my very brief opinion based on very brief experience with the Kestrel. (adding in some extrapolation from using my homemade slings) This is based on me being 6'3, 190lbs, 32" waist, larger than average thighs, living and hunting the majority of my time in south Louisiana, with the majority of those hunts in 60*F+ weather, with hikes between .25-1miles each way, taking 1-2 out of state trips to hunt public land with longer hikes, and colder weather. I use SRT or 1stick to get up the tree. I'm leaving out pros/cons in relation to anything outside of GW and Kestrel, so view the info through that lens.
Here are basic pro's and con's of each for ME, and scenarios they'll be more preferable over the other, for ME:
Weight - Kestrel
Packability - Kestrel
Ease of donning - even
Ease of adjusting - even
Ease of climbing - Kestrel
Ease of rappelling down - even
Ease of maneuvering around tree - even
Ease of rotating inside saddle with feet still - Kestrel
Ease of taking a shot over saddle to my right - Kestrel
Physical comfort that results in less fidgeting/movement to adjust - GW
Overall comfort in 60*F plus temps - Kestrel
Overall comfort in below 60*F temps - GW
Noise to the touch/sliding across fabric - GW
Multi purpose use (hanging cameras, presets, etc) - Kestrel
If it's above 60*, I'm not using the web, regardless of any other conditions or circumstances. It's simply too warm for my style of hunting. That being said - the Kestrel will get the majority of my run time.
If I'm hunting in cooler temps, The potential for longer than a 3 hour sit exists, and it's less than half a mile walk in, I'm taking the GW.
If I know I will be hunting all day in cooler temps, and I know my destination regardless of distance, I'm taking the GW.
If I don't know my destination, and the walk is longer than half a mile, I'm taking the Kestrel.
I personally don't believe one tool covers all scenarios and circumstances and hunters. Hell, if I had a place I could leave a climbing stand at the base of a tree with no branches year round, and the tree was in the perfect spot to kill a big deer, I'd buy a climbing stand and do just that. I am just making the point that you shouldn't place too much emphasis on another hunter's experience with details that are subjective.