I've got an RK37SC (with shuttle shift and cab) and use it a lot and REALLY like it. The FEL is heavier duty and better built than others I've looked at of similar horsepower. I've given it a heck of a workout. I'm coming up on 500 hrs on mine.
I purchased the following implements and attachments along with the tractor from RK: the FEL and bucket, the 60" Top Dog Granite Grapple (VERY well made and I use it a LOT. It stays on the FEL 98% of the time), third-function kit (which supplies hydraulic power to the grapple), 5 ft KingKutter Rotary Cutter (AKA bushhog. Special ordered, heavy duty model with 65 hp gearbox), 72" KingKutter Rear Blade (special ordered, heavy duty 6-way adjustable), Carry-All frame, and Boom Pole.
From Good Works Tractors, I've bought the following: Speeco E-Hitch Cat-1 Quick Hitch, and the GWT Heavy Duty Wrecker Stump Bucket. I also purchased from PTO Link their SD System which is a quick connect/disconnect system for PTO shafts.
My biggest complaint with the tractor (and it's a minor one) is the cheap, flimsy rear-view mirrors. The mounting rings on the mirrors are just plastic and you can't tighten them enough to keep limbs from knocking them out of adjustment when I'm bushhogging around trees and brush. I'm looking for some heavier duty metal-framed mirrors.
Mine has the R1 tires on it because the vast majority of my use is not on turf or pavement. It's amazing the size and weight of things that the FEL and grapple have been able to handle, lift, and move. We've used it several times cleaning up LOTS of debris from three tornados that have hit our farm and surrounding areas over the past two years and its capabilities have amazed us.
My across-the-fence neighbor has the same sized tractor from the "green company" and my RK37 is very noticeably better and stronger built, but the green one cost a LOT more money.
I can highly recommend the RK37. I chose the shuttle-shift version over the hydro-stat version because I do a lot of heavy bushhogging, tilling, and grading and small hydro-stat tractors are much more prone to over-heating in that kind of use, compared to gear driven shuttle-shift ones.
Hope this helps.