If you search this site you will find several, long, discussions on this exact subject!
To cut a long story short .......
Both will work just fine
if the hydraulics are getting a bit tired then opt for the slightly thicker (but only slightly) 80W90 Gear oil (actually much the same viscosity as SAE30 motor oil, but with different additive package)
However if you live in a country where you have to dig the tractor out of the snow to find it 3 months of the year, opt for the thinner UTO
UTO's have 'all the additives' for both Hydraulics and for gear operation and are therefore more expensive than standard gear oil, (and much more expensive than simple
hydraulic oil). but foaming is less of a problem with UTO than with Gear oil.
DO NOT use Standard Hydraulic oil in a gear box, it will cause premature death due to not having the all important 'extreme pressure' and 'Film Cling' additives required in a gear box and Diff.