To my surprise, I like the older translation better. The newer one feels a bit bland, and over-explainy (e.g. I don't actually need to know the specific phonology of the "Hamburg accent" Mann refers to, and describing that doesn't make much sense when I'm not reading the dialogue in German). I should probably add the other translation as its own book and switch over to it.
Meanwhile, I was very amused yesterday to learn that this story of a man who thinks he's going to a sanatorium for three weeks and ends up there for seven years was originally conceived as a novella, and in the end it took Mann 12 years to write the 750-page doorstopper. Life imitating art imitating life and so on.