I've adapted best to my 10x42 Noctivids for all round birding only bins. An ideal match for my eyeglasses in terms of eye relief and a perceived 'wide', immersive AFOV. I keep the eyecups screwed all the way down. I'm comfortable with 10x, and my interest in greater magnification is simply aesthetic. Its a lovely view, and I have no complaints. When I'm out painting, I carry a smaller pair, either 8x25 Zeiss pocket, which do the trick, or a pair of 8x30 Swaros, or Nikon MHG. The Nikons were misplaced for several months, so it was the Swaros until recently. The Nikons are a slightly better fit for me, though.
If I'm carrying a scope, I opt for 8x42 or 8x32, for a steady view with one hand, and sometimes I'll take an 8x32 with me when I'm out painting, if I think its a birdy spot. When hauling a backpack of art supplies, a 42 mm bin is less desirable due to size and weight, and I find myself choosing the 8x32 EL instead of an NL, for those reasons.
So I have an 8x42 Zeiss SF which is relegated to bird feeder duty most often, and the NL 8x32 usually sitting in their case. Both excellent bins, but currently not in rotation very often for reasons mentioned above. When I do use them, I'm always happy to partake of their wide and sharp views. Ironically, If I could only have one bin, it might be the Zeiss SF 8x42, but since I've got a buffet of use-specific choices, it doesn't get used as much as it would otherwise.
Conclusions: I agree it is all subjective. All the bins I mentioned give me a full view to the field stop with my glasses on. My preference. There are many otherwise excellent bins in the world that won't do that for me. I find I do prefer 32 and 42 over smaller sizes for viewing comfort, but will opt for smaller when circumstances dictate. Better with than without.
-Bill