LS R3039, Power King 1614, Simplicity Soveriegn 75th Aniv model.
I have had the JD 17AT dump cart for about 2 years now and am pleased with it. It is holding up well and still looks new (dirty, but new). My only complaint is that, when dumping, you still need to shovel much of the load out. This is a problem with most dump carts.
John Deere 750, John Deere X540, Wallenstein BXMT3213 chipper shredder, Befco bush hog
I have the 10P cart. I use it all the time with my X540 for hauling fire wood, to catch and haul mulch from the chipper/shredder, to haul tools, etc. It's been a very useful purchase that I get a ton of use from. I could probably use a 17P with the X540 but I had a smaller mower when I bought the cart. The 10P is also small enough that I can move it in position by hand when it's fully loaded with mulch, which might not be easy with the 17P.
I use an MC 519 cart (two point hitch if I have to do alot of backing in tight places) and a Sears dump cart for other projects. If I were buying an new Deere cart for your mower I would go with the 21 cart and probably would carry smaller loads leaving the tail gate off. Easier to dump without the need for shoveling the tailings. When carrying light stuff you have a bigger box capacity too.
I have owned both. They are great for loose items and firewood. They're virtually indestructible, but they stink for hauling loam, gravel, sand, etc as they wont complete empty and you need to shovel them out.