Oooh. I do love Or Co Dadi, mi fra Poco and in fact the work of the chorus in Il Trovatore is flawless on Verdi's part throughout . My personal favourite might not strictly be a chorus chorus but is by far my favourite piece with choral work in all of Verdi (and overall in opera as well) as it's just so cleverly done
I really don't know how Verdi managed to put sarcasm so exactly into musical form but he did. Other parts of Un Ballo in Maschera have great choral moments as well Verdi really had a great grasp on Choruses. Of the Verdi operas I have seen so far I don't think there is a weak choral moment in them at all.