I think it was in a James Yeager Youtube video where he is reviewing the XS sights that he tells the story of him putting out several guns on a table in a combat shooting class for them to choose. Most have the XS sights and a few have 3 dot sights, and the class switch guns repeatedly during the class. He said by the end of the class, no one wanted the last remaining guns, which had the 3 dot, all preferring the XS. He didn't tell the class it was an experiment or anything, but the results of the experiment showed a natural preference for the XS sights in a A:B test of sorts. That result, and the voice of others on Youtube, most of whom I assume aren't on the XS payroll, is leading me to try the 24/7 XS sight with tritium front and rear.
Now of course, almost all admit the 3 dots are better for target shooting, especially vs. the Big Dot version, but for defensive combat use, the XS sights are apparently much faster at target acquisition, and getting the bullet into critical center of mass (not necessarily bullseye). Fast is good.
Previous to this, I was considering the TFX Trueglos, as the fiberoptic is very bright and conspicuous when there is a secondary light source. I'm still a bit torn between XS and TFX. I think these are two of the cutting edge designs. I may go with the smaller XS, since it would be better at target and distance shooting than the Big Dot, with the idea that maybe you don't need the sights as much close up, but do at distance. Regardless though, I've seen some great shooting with the Big Dots, even when they cover up the entire bullseye mark, which they do.
I think the rear XS sight is probably better for fast acquisition and peripheral (albeit very small) vision than the I dots which leave a more classic window to peer through at the rear. They apparently are also more comfortable IWB than some taller, more jagged rear sights. This can be very important for carry purposes I suspect, especially appendix carry.