Timequake is one of the few I haven't read more than once, but also one of the ones I would most like to revisit, now that I think on it. I had the feeling that it would "settle". I remember feeling that it was disappointing when it was the newest and latest after years-ish of waiting. Now that there are no others and the context is reduced/simpler, and the expectations appropriately tempered, I've got this weird feeling that I'd like it a lot more in rereading it now, and this sense that there was at least one theme I missed that first time.

(Doesn't help that I'm also in that team of people with a strange disjoint out-of-time relationship to Vonnegut's novels having read Breakfast of Champions to early to understand most of it, and wandered the rest of the catalog randomly via my parents library and then the actual library as I grew older. Timequake was the only one released in a time where I was able to anticipate it, and given opportunity to hype it so much in my own head.)

Welcome to the monkey house takes the cake for me.

God Bless You, Mr. Rosewater is actually my favorite. Hope you get to it! Some of his later books, as you note, just got so preachy and overwrought, I couldn't get through them.