I preferred Tom Hulce because his Mozart was so genuine and you could see why people might actually like him and champion him, Gillen's Mozart somehow comes across to me as both unlikeable and pretentious

Precisely. It's sad, because everything else about this production is superb, and I'm fine with alternate interpretations of characters, but Gillen's Mozart being so relentlessly dislikeable, as if someone, either Gillen himself or the director, decided to take Salieri's "this obscene child" from the introduction scene as saying all that is to say about Shaffer's Mozart, which is a shame since it robs the story of layers.

Otoh, it also shows, as I said to laurashapiro below, how good Hulce was, which tends to be a bit overshadowed because of Abraham's (deserved!) Oscar.