Celeris. I ride 4/5 horses a day with them since 2013 and they are in great condition!
I used my Tattini boots for over a year riding 4 horses a day, and walking and lunging in them. They are quite cheap compared to other brand but for working and training they are just perfect. Zips are really good, I never had to fix or change them. They cracked at the sides of the tip, but that was my fault too, as I did very low (to none) manteinance.
ariat as well as la mundel, and try to get ones with a second layer of leather on your calf
My Treestep Donatellos have help up great for 5 years, just clean them regularly and will look as new