utahmule,
I have the MX6 and am happy with it. I like the two deck approach JD has used. Its very easy to clean the top of the cutter after use with a broom, water just runs of the deck and does not puddle up anywhere. I don't see how it will ever rust out from the top. John makes a good point about getting a hole in the lower deck. I have hit stuff and seen the top deck bounce a bit. /w3tcompact/icons/smile.gif And I have chewed a couple of rocks maybe 5 inches in diameter into much smaller rocks without any problems.
I don't mow alot of land or often but what I mow is full of rocks, sticks, timber slash, and stumps. And I hit the rocks, sticks, timber slash and stumps. Not real often but more often than I would like. The only damage I have done was to the wheel assembly on the MX6. I bent it when I backed up with the mower lower to the ground than I thought. The wheel caught a hole and got bent a bit. But that is hardly a JD design/build problem. The %^&*() hydraulic toplink had let down a bit and the mower was lower than I thought. I pay real close attention to that wheel now a days! /w3tcompact/icons/smile.gif
The MX6 is supposed to handle two inch diameter wood. I try to keep it at one inch or less. I just wanted the extra to keep me covered when I do hit something.
I would look at the price of the cutter, the thickness of the deck and sides, the weight of the cutter and the price. /w3tcompact/icons/smile.gif I doubt you could really go wrong with any of the three brands....
Have you thought about slip clutches? If so you might want to check on how easy it is to do PM on the clutch.
Later...
Dan McCarty