I've currently got 3 6x36's on hand. You might say I like that particular scope.
Anyway, over the years I've occasionally and informally compared the 6x36 and 6x42, but only in various stores, which really isn't exactly a critical comparison.
So, about a month ago I got a good deal on a 6x42 VX3. I bought it to see if the hype here on the campfire about this scope had any merit.
I compared the two over several days in a variety of lighting, evening, morning, nearly dark, bright sunlight, on a variety of objects, animals to lettering.
What I found is my nearly 56 year old eyes can discern NO difference between the two. I doubt the larger exit pupil of the 6x42 has any meaning for my eyes. The 6mm exit pupil of the 6x36 is probably all my eyes can realistically use. Of course I couldn't see the difference in my 40's either. I find the much vaunted "eye box" superiority of the 6x42 to be non-existent for my eyes as well.
So really, at least if you're over 50, unless you just want a heavier, larger, more expensive scope, I'd steer clear of the 6x42.
My .02
