Lots to consider depending on your use and thickness of your wallet, most is personal choice. Bigger diameter wheels slightly smooth out bumps in rough ground, but in the scheme of things may not be particularly noticeable, 2800 and 3100 both have external oil filters for ease of maintenance. BB has nearly twice the thickness deck, and a lot heavier machine overall, weighs ~160 lbs more than the other two, whether this is a plus or a minus depends on your use. The chute lift on the BB would disappear around my trees, it is probably removable. Base engine hp higher in BB, then ZT then Raptor. When cutting long grass going slow, there can be a slight advantage with higher hp. (All the same engines, different carbs) The BB will use slightly more fuel, may not be a consideration for general use, but commercial use worth factoring in. Optional electric deck lift on BB. Check out the seats, what do feel more comfortable in or what moulds to you better. Parts prices, same engine, same drive, so only deck/frame to consider, probably not a big one to worry about. Warranty differences, I haven't looked. YMMV. Whats the price point of each, how many acres/what type of ground do have you have to mow, do you need/want a bagger? I'm sure others will chime in with more info.