I've got 3 standard U.S. residential toilets in my house--all
different models but all bought at the same place a few years back.
Two of the three work just fine. But the third one stops up with solid
waste probably two out of three flushes. (It usually clears after 2-4
extra flushes, but sometimes requires a plunger.) My contractor
assures me that the waste pipes into which the toilets empty are all
the same size, so it seems clear it's an issue with this toilet.
Looking at the S-pipe outline on the lower side of the toilet, it
seems as though the path from bowl to floor waste pipe is pretty
similar on all three toilets. But only this one gets stopped up. (And
yes, the same people are using all three toilets.)

Are the internal workings of the bowl-to-waste-pipe path standard from
company to company, or is there a wide range of variations? How can I
replace this toilet and be assured that the same problem won't result?

Jim B.