From my IPSC and Action Pistol days I learned the answer....
PRACTICE AND USE BOTH.
Interestingly, while EVERYBODY in IPSC back then seemed to favor the Weaver, I basically tried it when I started, (Jeff Cooper was my HERO) then drifted "naturally" back to the Isoceles, and for a while was about the only one using it as my main stance...(except when I was using a barricade, then the Weaver seemed to be better....)
...until I started shooting moving targets in Action Pistol, then EVERYBODY started using Isoceles just about exclusively. Swinging and hitting a laterally moving target seems naturally "easier" than with a Weaver. Shooting MORE than three targets (like the six plates) seemed easier with it too... Get a firm footing facing the center of of the range, then swing through right to left then left to right, without moving your feet, 6 rounds in the approximately 10 seconds at a target moving 6 feet/second through the 60 feet(which incidentally teaches you a LOT about lead....)with a Weaver you will only be in the "optimum" stance for MOSTof the time the target is visible. while just pivoting your hips can cover the whole range with an isoceles comfortably.
But I discovered, almost on my own as one of those "epiphany" moments, during a goofy practice drill, (and then found out from a Police Instructor friend of mine that used to travel with Massad Ayoob that what I discovered was NOT "new" at all...)
Try this....Stand in the Isocelese, aiming at a target directly in front of you, THEN try to engage a target 90 degrees to your left...QUICKLY, withour moving your feet. Guess what? You are in a PERFECT Weaver! IF your hips are supple, (and you are YOUNG
) you can ALMOST engage targets directly to your REAR swinging to the left (for a right handed shooter) with the same Weaver!
Then swing the other way, QUICKLY, through the perfect Isocelese, engaging targets to the front, and swing through, and to almost 100 or more degrees to your RIGHT, you can engage targets, again without moving your feet, with what is actually a REVERSE Weaver...with the LEFT arm almost as straight as a rifle stock and the RIGHT bent....with your head down on the left arm using your right eye just like old Mr.s Weaver and Cooper intended....
SOOOoooo....learn the Isosceles, and also practice the Weaver, and you can QUICKLY and accurately cover almost (but not quite) 270-300 degrees around (OK 200-250 or so to us stiff "getting old" farts) if you are surprised without moving your already acquired FIRM footing ....
What I do to this day is practice BOTH, each time I shoot about any handgun I START with a slowfire group Isoceles, then I do ANOTHER with Weaver...then if I do more, I do the standard drills varying with both...
But what is strange, when I was younger, I could shoot better groups with the Isocelese, but it seems as I get older, the "push-pull" Weaver does better for me..I seem to "wobble" more with an Isocelese the more I try to shoot a slow group....
There will be times when one or the other will be better for the specific situation, so be proficient with BOTH, and you will NATURALLY assume the "better" one in the proper situation without thinking about it....