But, I do have a bit of experience with both of these. I loved the Estwing from the first time I saw it... looked cool, indestructable, etc...
until the first time I laid into a piece of hardwood with it. Ouch! nothing but pain from my hands through my elbows. I never spent any time sharpening it after I got it, it may have helped some with the impact vibrations, but they were still pretty severe. Mine got stolen and I did not replace it.
After this I bought the Back Paxe.
I have carried this thing all over the world, including combat many times over the last decade. I have never cut down a large tree, or built a log cabin with it, but IMHO this is one of the best pieces of equipment I have ever owned. I took my DMT sharpener to the edge back when I got it, and within a minute I could shave hair off my arm like I have with few knives from the manufacurers merely by removing the burr from the edge. I've never had any issues with my edge chipping, though there are probably many here who have used theirs harder. I also liked the flared end on the handle, very comfortable, and allows you to relax your grip just a little.
I have been meaning to get one of his bigger brothers for years, but just did not really have a need. I don't think the Estwing Camp Ax would out perform my Back Paxe. Even IF it did take a few extra swings to get the job done I know I would not be in pain.
Even IF you could argue that the Estwing was more durable (I have doubts) the Fiskars:
#1 will not beat you up
#2 much lighter without sacrificing any performance
#3 less susceptible to corrosion
I am not sure what the price differences are these days, but I'm sure the Gerber/ Fisakars are competetive.
I will however make a zombie disclaimer... The Eswing begs to be modified into a zombie dispatching apparatus.