With some cigars size doesn't matter much, with others it matters a lot. Personally I find Padilla Miami to be a lot better in a smaller ring, and Camacho Corojo to be better in a 50+. I find the thinner Padillas to be more flavorful, and the thinner Camachos to simply not taste the way I think they should.
Many (most?) NC cigar makers try to adjust the blend to minimize differences between sizes. The result is that in many cases it can be hard to tell the difference in taste between sizes.
I'm no expert on Qbans, but from what I've heard they tend to use the same blend for the whole line, resulting in substantially different flavors between sizes as the different proportions of wrapper (and binder, though it's less important) to filler change the taste of the cigar.
Bigger ring sticks tend to burn cooler at the same rate of smoking than smaller ring sizes, so your personal smoking habits also have an impact on which size will be most enjoyable. Fast smokers seem to like 50+ rings & slow smokers tend to prefer coronas/panatellas/lanceros/etc.
At least in the US, I suspect the movement towards bigger ring cigars may also have something to do with the movement towards fuller bodied cigars. Burning cooler can take some of the bite out of a strong cigar, and in cases where you've got a powerful wrapper diluting it a bit can make the cigar milder.
I think the best way to go about it is to just try each approximate size a cigar comes in & then decide which one you like best.