First, I suppose you mean the
BX23? That's a Sub CUT and the others are CUTs (compact utility tractor), the CK20 is a small frame CUT and the CK25 is a medium framed CUT. Lot's of difference.
I don't know what your uses will be for the tractors, but I can easily say that the CK25 is enough higher-priced than the CK20 not to by the 25. It will allow you to use the next size up in mowers and other 3pt hitch attachments (5' vs 4') and has a lot of extras like telescoping hitch arms and stabilizers that make hook up much easier.
As far as quality goes, I don't think Kubota has anything better. They are both very good quality. Daedong engines have been made since 1949, they know how to build engines. They have built tractors since the 60's. Kioties are comfortable, well laid out with platform frames instead of ladder frames (strong, but not as nice as a platform).
I have Kioti, so unless you can get a much better price on a Kubota, you'll get more, usually, in a Kioti for less money.
The
B7510 Kubota is the comparable tractor to the Kioti CK20 by the way. You'll get more clearance with it and the Kioties than you will with a
BX23. You should be able to get a CK20 TLB in the neighborhood of $17K to $17,500.
John
John