On my JD 4120, it would probably be the canopy I made that fastens to the top of the ROPS with (4) bolts. I used a canvas-covered wood frame. It is light wieght and I can have it on or off in less than (5) minutes. The canopy is larger, lighter and thus more effective than most store-bought ones. A primary usage of this tractor is open-field mowing in the summer and it can get mighty hot out there under the mid-day sun. Operating this tractor with the canopy installed is nearly as comfortable as an AC cab. It was great not to have to pay for one of them, and still have the versatility of quick removal for work in the woods, and so the ROPS can be folded down to fit into std 7 ft garage doors, etc. The hour or so I spent building that canopy has been paying big dividends for 5 years now. It also does a nice job keeping me dry when I get caught out in the rain. A close second would be the tree scoop I made that bolts to the bottom of the bucket. This is simply a piece of 12" x 3" channel iron that is about 30" long and bolts flat under the center of the bucket. I used (2) of the toothbar holes (thankfully I dont have one of them installed), and drilled a 3rd hole on center, 8" back to attach with (3) 1/2" bolts. This attachment also took under an hour to build and worked wonderfully to scoop and move about (25) 5-10 ft tall blue spruce last fall. I cant wait for the ground to thaw out this spring so I can move a bunch more. Like the canopy, I didnt need to purchase any materials (I had the channel and bolts laying around the barn), so it was just an hour of my time required to save weeks of back-breaking labor with a shovel and ball cart to get them trees moved. In my opinion, a "free" mod is a much better candidate for "best" than one you pay for in this uncertain economy.