Goodness, they are difficult for me to remember from most other entries and even in 4 not many stand out. I usually use my own or have saved edits to various homes I would use.
I suppose my favorite is Vlad's mansion. Over the years, I have greatly expanded it with many basements levels and new rooms. My most ambitious expansion yet was a floating room for an onsen when SE dropped.
Some honorable mentions for 4 would be the large vacant manor in Strangerville, the shipwreck from IL, Hound's Head from C&D, and the Goth house (though I never play with it).
I think I was even more nomadic in the other entries, but I really liked one of the rural homes in Sims 1. I think it was called something farm. Anyway, it was small but came with plots of soil. In 3, I remember liking the largest (or what I remember to be the largest) home in Appaloosa Plains. I really liked that world anyway. In 2, I think the two witch sisters' home from Apartment Life.
*edit
I looked it up. Sims 1 was Appleview Farm, an Old Town lot apparently. Sims 2 was 218 Bay View Drive, home of the Cordial family (no wonder I did not remember with a name like that, there were three others nearly identical). Sims 3 was an amalgamation of the Lexington and Six Gables Stable in my mind, but my favorite was Six Gables Stable.