Get a commercial grade in whatever brand you end up choosing. My first zero turn was a Cub Cadet, residential, and although it worked out okay, it was just too lightweight for my rough ground. My current mower is a Husqvarna, commercial rated, and it's been practically trouble free for 6 years now.
Buy from a dealer, not the big box stores, although sometimes the big stores will offer good deals. The problem though, is that the mowers they sell are sometimes downgraded in the engine department, and other features.
The thing about the JD's is that if you take care of it, it's going to hold it's value.
