I opted for the 42mm even though the 38mm actually looked fine on me as well as it did for my wife.
However, that little bit of extra battery life was important to me, as well as many accessories that seem to be targeting or accommodating the 42mm versions.
It really wasn't a toss up for me between the iPhone 6 or 6 Plus either, as the 6 Plus had a true 1080p resolution as well as the Optical Image Stabilizer, which the 6 didn't have. It probably has a larger battery, but I didn't bother to check that one. I do have a bit of a hard time with it fitting in my pants, but I can't forgo that larger screen.
As my luck would have it, the 6 seems to have the ever-so-slight upper hand in the availability of accessories, compared to the 6 Plus, too.
My brother opted for the 6 at the time of the launch, and he regretted it after a few months and used his grandfathered JUMP! to upgrade to the 6 Plus, and I know I wouldn't have gone the other way back to the 6.
So, as I probably made the right decision in the iPhone, I probably made the right decision for the 42mm
WATCH. To each their own.