I vote front wheel size (in 4wd AG tire configuration).
20"+ rims is UT
anything under is CUT
This would mean DK50se and smaller, all the NX and DK10 series are CUT's. And the DK55se and larger, All the RX and PX series are UT.
For kubota, all the L's and MX's in their current line is CUT. All the M's are UT's
Deere (an this is actually how they have them listed), All 4x are CUT and all 5x and larger are UT
Massey....dont list tire specs. So only looking at pictures. They list 1700 series as CUT and 2600 and 2700 series as UT. And am betting that the front R1 tires on the 1700's are 16's, and the 2600's and 2700's get either 20's or 24's.
For new holland (their models are a bit confusing and no tire specs listed) but appears that all the Workmaster series and T4 and larger are UT, and all the boomers are CUT's. The exception is a "workmaster compact" which is ofcourse a compact
LS is as listed on their website. XJ, G, XG, and XR are CUT. K, XU, and P are all UT's.
Seems most of the MFG's that do differentiate on their websites, like Deere, LS, Massey, All of what they call CUT gets 16" fronts. All the UT's get 20" or more.