UT30 would I have slightly better blacks with all the lights out (0.02cd/m2 vs 0.028cd/m2) but the ST30 goes brighter & also has better contrast in all conditions
I think the UT30 is based on the S20 from last years range, it doesn't suffer from the green tint or splodges & the fluctuating brightness has been fixed on the latest firmwares for all models anyway
It also does not have cooling fans
IMO the UT30 is a good buy but after owning both the St30 is a lot better for little extra money IMO
If you can get an ST30 without the green splodge it is an excellent buy