If you're building any singletrack, climb trail, hybrid or anything smaller than flow get a u17 or 17g, don't waste your time with anything bigger or smaller, bigger machines don't have a collapsible track width and smaller like the e10 just doesn't have the breakout power. I've made both work but always think the 17 is the right tool for that kinda job.
I'm building flowy singletrack, and ive been offered to choose a mini ex to use for future projects with a company I do contracting for.
Locally, there is a company with a U55 Kubota, which I'm worried isn't small enough. Should I maybe swing for a different machine from somewhere else?
Just so you understand the numbers, a 17 is a 1.7 metric ton machine, so any 17 series from most of the manufacturers will be relatively the same. CAT numbering is a little different though, CAT labels theirs as 301.7.
The U55 is a MUCH bigger machine, 5.5 metric tons.