I have GH's and couldn't be happier. They make quality, long lasting, heavy duty, mowers. I haven't owned any newer Gravely's, but I think they make a very high quality line too. Both brands make lower priced but above average mowers as well. My preference is to get the best quality I can afford. Then take care of it and it will last a very long time. If mowing a lot of acreage, try to get the best suspension seat from either brand - they both offer top of the line air suspension seats (some of the best of any brands). Their seat prices will shock you, but you'll be spending a lot of time on the mower over the years and the comfort is worth it.
If you plan to get a front mount for a better ride, easier deck care, etc, I'd go for the GH. If just getting a standard zero turn, I would test both mowers on your property if possible, then make your decision. That's what I did years ago before buying, after having my mind made up (or so I thought). The tests on my property were surprising and I'm glad I took the time to do that.
