The Estwings balance and handle like a hammer. I love my tomahawk and double bit, but there is no getting around the fact that they are made like a hand tool.
For that reason, I didn't go to the extra expense or maintenance effort of leather. Rubber grips work just fine. I have been abusing mine for a few years now. Besides some scuffed paint, they are holding up well. The handles are dirty but look brand new otherwise.
The leather handles don't really age well unless you take good care of them. The rubberized handles hold up to almost no care, it is the same material as the hammers and I have seen them heavily used for decades with the only results being they get a bit less soft. I think the leather is more comfortable for some things but the rubber is cushioned and transmits less vibration.
In my experience the leather washers eventually shrink and get loose unless you can keep it well hydrated. I had a hammer, and saw others which through regular use and no maintenance shrink and get loose.
I like the leather, and it has a finish on it that is maintenance free. Theyre comfortable and durable, and can be repaired if it needs it in the long term unlike rubber which will eventually degrade. Most importantly, stacked leather looks great!
The leather looks nicer and easy enough to repair or replace.the synthetic is tough doesnt feel or look as good but I have destroyed the synthetic handle material and replaced it with leather on a few estwings that I throw.