Ideally corona or lancero. Wrapper to filler ratio = more flavor...In cigars with the same blend and wrappers, those with smaller ring gauges have a higher wrapper to filler ratio and, thus, the wrapper will contribute more to the flavor.
I guess I'm not enough of a cigar smoker (I'm not); I thought the OP was about jewelry. So I'm not versed in cigar circumference, but middle sized works for me. Puny cigars are nice and cheap and make a good short smoke, and Clint Eastwood did miracles for them in the old spaghetti Westerns, but they don't give much of a cigar experience. And the giant cigars, an inch across look so ostentatious, like a college kid at the horse track with mobster fantasies. Much depends on the flavor, though. I like them mellow.
When I was new, I was taught, and my experience has backed up, that the coronas are sort of an ideal size. They're thick enough to provide complexity and nuance, but thin enough to provide a good clarity of flavor. So coronas, coronas gordas and even toros tend to work really well for me. If I was designing an ideal size for me, it would probably be a 6x46 CG.
I also like lonsdales, lanceros and panatelas, and piramides/torpedos.
I cannot abide by ultra fat cigars. To me, they're uncomfortable in the hand and mouth and provide an airy and muddled experience. If the RG is greater than 52/54, I can really only enjoy them if they're figurados. I don't mind thicker cigars as much if they're pressed, but still don't want anything thicker than a 54, really.
That said, I know the ultra-fats are very popular, and there must be a good reason for it. I don't begrudge anyone their preference.