Personally, I am not a fan of longwings, so I went with the McAllister and am happy with them. Are you looking at shell Cordovan? If not, I am not a fan of the grainy texture of the walnut they use on the McNeil. I also prefer the sleeker look of the McAllister, specifically the single sole vs. the double.
I suspect others in this thread will tell you they prefer the McNeil.
Edit: Also, the McAllister is a balmoral/oxford, while the McNeil is a blucher/derby. Not sure if that matters to you.