Yep that's one tough choice ..... a 12 or a 20 ga USH.
Been down that path before and I don't envy you for a minute.
Drove myself absoulutely crazy.
In the end, I was fortunate to be able to do like Scibaer said....buy both.....the 12 for me and the 20 for my son.
Personally I still like the fit and feel of the 12. One day that might change.
They're both fine shooting guns and buying either one won't be a mistake.