Sounds like you prefer the isosceles stance, whereas your cousin like the Weaver. The "best" stance/grip is likely the one you shoot best with and most accommodates your style of shooting. The 1-eye vs 2-eyes thing is another thread...
As for me, I like informal target shooting with a double action revolver. When shooting 2-handed, I found that the isosceles stance works better for me, for a couple of reasons:
1. The grip/stance feels more neutral. I feel too much push/pull of the gun with Weaver. Push/pull might control recoil in rapid fire - I dunno - but it's hard to get the 2 opposing forces consistent enough for target work.
2. For combat action type shooting, I seem to be able to quickly move to either side easier when using isosceles.
3. When shooting a DA revolver in DA, I place the 1st joint of my trigger finger over the trigger. To get this, the gun is gripped such that the barrel of the gun isn't in line with my arm, but at an approximately 30degree angle, which is about what it would be anyway in an isosceles stance.