My first thought was he was prying with it, most 1/4" factory blades are going to handle chopping chores, but will not perform as well as a custom or bend instead of breaking. My 1st vote is for the old reliable 1084, with a differential HT. The problem I think is he's prying in some manne,r like getting it stuck in a large sappling. Without knowing exactley how he broke it makes it harder to answer the question. My 2nd would be for W-2 would be execellent, with the proper HT, it is kinda tricky stuff. L-6 should do well, but I have no experience with it. I have tested all of the W-2 blades I've made so far, not to destruction. The last one I made is going to be abused by the guy that's getting it, not to destruction (he likes it too much), I offered that if he would abuse it, I'd make him another one if needed. Provided he didn't chop rocks, or pry with it, I would think with a differential HT it should be OK (if I'm off base here, someone please correct me), but it still has limits as they all do.It shoul dperform better than any manufactured blade he's used, for sure.
See where he had issues with the ones he's used, also check his hands, see if they are larger than normal, it could have some bearing in the way you need to make it, and if they are huge, it'll help you make it a bit more comfortable for him. Checking a customers hands impresses them for some reason, the only reason I do it is because my hands are in the huge range, I have to get 2X gloves at the very least XL with material in the back so they stretch.
1/4" should work with a differntial HT, check on that to make sure, and maybe some other guys can chime in to make sure I'm on point! Rex