I think it depends upon the gag as well and not just the scene. Most people think of ball gags but there are also dental gags, open ring gags, bit gags (pony-play), and odd novelty gags ( link ). I think some of those models are *intended* to be humiliating.
Personally, I like cleave gags the best. It's simple and easy to use a man's neck tie or lady's scarf and wrap it around your partners head as a quick make-shift gag. It fits in very nicely with kidnap fantasy scenes. Although I've never done it, I have seen some very aesthetically pleasing shibari cleave gags. For me, it is the sound you make in a gag that's the turn-on. So for me, it's not just visual, per se, but acoustic as well. Can't say if anyone else agrees though...
Personally, I like cleave gags the best. It's simple and easy to use a man's neck tie or lady's scarf and wrap it around your partners head as a quick make-shift gag. It fits in very nicely with kidnap fantasy scenes. Although I've never done it, I have seen some very aesthetically pleasing shibari cleave gags. For me, it is the sound you make in a gag that's the turn-on. So for me, it's not just visual, per se, but acoustic as well. Can't say if anyone else agrees though...