Ernest G I don't know anything about Umberto, but I think Ellis has just the right amount history against great characters. I've been googling the historical places and characters and found all kinds of cool stuff. Places/people I thought were fictional were factual. My gosh, I found pictures of the chapel over Saint Winifred's spring and live cam view from Shrewsbury castle of the Severn River.
S.J. Arnott I quite like Mr Eco, but you do get the impression that he takes himself quite seriously. I think Ellis Peters stories are better, if less cerebral (mostly straightforward mysteries with a few twists thrown in) and Cadfael himself is a very engaging character.