First, the CK20 and
B7510 are both excellent machines with 21hp diesels. The
B7610 is nearly a clone of the 7510 but with 24hp. Most people who buy the CK20 have seriously considered the Kubota 7510 and as you can imagine the machines are more similar than different. However, there are some potentially important differences that could affect your choice.
I will ignore for a moment the issue of price. That seems to vary by dealer enough that sometimes you get a better deal on a Kubota and sometimes on the Kioti. Price is also an issue with resale. I would imagine that the Kubota would, today, be easier to sell. That may change if Kioti continues to build it's reputation. Again, not an issue if you are planning to keep it for 10 years.
The Kubota is lighter by about 600 pounds. Put another way, the 7510 weighs two thirds of what the CK20 does. That can either be good or not so good depending on how much finish mowing you plan to do. Light is good for finish mowing (generally). The 7510 has another advantage for mowing if you want a MMM. The 7510 turf is a great deal with the MMM adding as I recall only about $500-700 to the price of the base tractor. The MMM for the CK20 will set you back well over $2000.
The CK20 is heavier which is generally a plus for "real" tractor like work such as plowing, box blade, FEL etc.
Features are pretty similar though the CK20 has position control while the 7510 does not. Nice feature but the Kubota guys obviously live happily without it.
Lift capacity for the 3PH is slightly higher for the Kioti.
The matching KL120 loader for the Kioti has considerably more lift capacity (at pivot pin) than the Kubota LA302 (1074lbs vs 770lbs) while the comparative breakout forces are pretty similar. The Kioti loader max lift height and clearance with bucket dumped are both about 18 inches higher than the Kubota. Kioti has a 54 inchs bucket compared to 48 on the 7510.
The Kioti KB2365 and Kubota B4672A Backhoes are pretty closely matched and are both subframe mounted.
Overall, they are both extremely well made and capable machines for their class. I was all set to buy the Kubota when I ran into a great deal on a barely used CK20. I have no regrets but I am sure I'd be happy with the Kubota as well.