While 38s are nice, 42s are more attractive to me. Most of my watches are mid-40s or more.
I chose the 42mm Watch for the way it looks on my wrist, legibility, and longer battery life. The 38mm looked fine in my wrist but fell short on the last two preferences. With its better battery life, I'm slightly tempted to add a gold 38 S2.
I'm probably not on my own when I say I didn't realise the difference in size between the two. It really is significant. For fitness purposes the 38mm makes sense, otherwise it has to be the 42 for me.
I bought a second hand 38mm first gen Watch and I regret it ever since.
In my defense it was to get familiar with the Watch until series 2 came out, but that one didn’t convince me to upgrade.
I will definitely get 42mm series 3 when it comes out.