For the last 2 years I have worked with 10"sets of rings. Recent experiments with near 12" (TCC Wonderful rings) is making me question whether the larger rings, are actually more deceptive, for the various ladder moves and optically deceptive unlinks. I'm using the thicker 3/8 guage in each.
Traditional advice says 12" are "for stage" but I'm wondering if they are inherently more deceptive - what do others think?

If so, then would it follow that something like Ninja Rings must therefore be inherently the least deceptive variant?

Good point - if there is any difference between 10" and 12" (and I'm genuinely unsure) then I think it only applies to certain moves, and also related to the thicker 3/8" gauge. I think the Ninja rings are brilliant, but I don't think the "ladder" moves are common neither would you try some of the slow optical unlinks at such close quarters?
I realise this is a slightly "perfectionist" question, actually triggered by the use of an oversize ring, which is definitely slightly more concealed in the larger diameter, but it has made me suspect there may be other differences in deceptiveness as the diameter increases, particularly for smaller, more intimate, audiences. If larger rings were somewhat more deceptive for smaller audiences this would turn accepted wisdom on its head when choosing size of ring set.

I don't believe the sizes of the rings add or subtract the deceptiveness. Larger rings can be seen better from a distance. Probably the reason why Pop Haydn uses 15 inch rings for his comedy routine.

The thicker the ring is in proportion to its diameter does make a difference. The thinner guage rings create a much better illusion of being linked/unlinked than the thicker guage. The 15 inch rings I use are very thick, and the illusion of two rings being linked is not very good from even a distance. I have to keep them in motion as much as possible. The tradeoff is okay to me because the 15" rings seem to have more impact and perceived importance on a full stage, and also seem more gripping for the audience in a parlor situation.

I have a set of 4" or 5" rings I bought as a kid, and I would think that with the proper handling and showmanship they would be just as effective as any other size, as long as the audience can see them.

I started with 8" rings as a teenager, and up-sized to 10" rings as an adult.

As with some of the other replies, I was more concerned with audience visibility and how they felt in my hands.

I never really worried about deceptiveness, and I never really felt like having larger rings would have improved my performance. I think the sound (and the fact that the rings have an innate beauty) is a much more important part of the illusion.

THAT is an interesting observation from Pop. I didn't realize that thinner rings are more deceptive for creating the illusion of appearing still linked after the move.

I used 10" rings for most of my career, a set of solid stainless steel rings by Merv Taylor. When I became "Pop" in 2005, I began to feel that the rings were looking small against my large black frock coat. Jon Stetson gave me a set of Owen's hollow, stainless steel 15 inch rings that he would no longer need, as he had become a mentalist. They were very thick, and I found that the illusion of two rings being linked and then melting through each other which I had emphasized in my original routine no longer worked as well. The audience could clearly see the rings were no longer joined, and were just held one behind the other. I began to put more attention on the crash links and other parts of the routine that were less impacted by the visual illusion. With thinner rings, the illusion was good even at close range. With the 3/4 inch rings, I had to keep the rings moving all the time and give the audience less chance to look at the two rings "interlocked."

I found that the thicker rings looked more impressive during the crash links than the thinner rings, and that in general the bigger rings made more of an impression and carried more of a sense of importance than the smaller, thinner 10" rings. I now prefer the impact of the larger rings, even though they do not have the same deception for some of the the "melt through" moves. It is a trade off, but one that I accept.

I think Pop has articulated what I suspected, it is the "melt through" moves which are most affected. I suspect the proportion of thickness to diameter plays a part but the other variable is the shine and polish/gleam on the rings. I favour a more matt, satin finish for visibility but have to accept that a more polished finish, under proper lighting makes the delayed/melt through moves more deceptive.