I wasn't expecting it, but the Basilica of Aquileia was astounding, one of the finest churches I have been in during all my World Heritage Site hunting.
As the other reviewers have noted the highlights are the mosaics on the floor which cover the entire surface of the Basilica. However I think I had an even stronger fondness for the incredible 12th century frescos in the crypt below the apse. The wonderful pastel colours and expressive paintings really left a mark on me, not too dissimilar to the feeling I had when leaving the Scorvegni Chapel. All in all a truly magnificent site. The fact that there are the scattered remains of a prominent Roman town strewn around this magnificent building only serves to amplify its impressiveness. I rather enjoyed walking amongst the ruins and partially restored columns whilst eating an ice cream, in fact there are very few things I could imagine that are as pleasing as this.
Even in a region which is almost drowning in cultural treasures, the Basilica at Aquileia stands out as a highlight, and it is hard to think of a bigger compliment than that.