Overall, I prefer the 42mm over the 38mm for a number of reasons.
Despite the same ppi, the larger resolution and screen does make things easier to read. A larger screen made it easier and more accurate for me to tap things on the screen, as I found on the 38 I would often end up hitting the app next to the one I wanted.
The battery life is much better as well, and it was somewhat surprising that Apple understated this point so much. On my 38, it would regularly drop below 40% (usually between like 38-33%) whenever I took the watch off to charge at night. My routine was basically putting on the watch first thing when I wake up (maybe around 8:10-8:20am) and using it the entire day, only taking it off to shower and then putting it back on right away, then it goes on the charger somewhere around midnight.
As mentioned, I got my 42 over the weekend, Saturday to be specific. The last three days I woke up around 7:20am, worked out for 30-45 mins with the workout app on, took the watch off when I went for a quick shower before putting it right back on again. After that my day pretty much went the same as before, though of course the number of notifications that I get and calls that I may take on my watch would vary. Last night when I put it on the charger, it was around 49-50% battery. So despite being off the charger for an extra hour and using the workout app for 30-45 mins, I would still end the day with around 10%+ battery more than the smaller one, so it could be entirely possible that I get 15%+ more battery if my use case had stayed relatively the same (no workout and waking up later.)
The 42 is definitely bulkier and less subtle than the 38, which makes it stand out more. The other minor inconvenience is that I feel that the sports band on the 38mm fit a bit better on my wrist; it felt just right at the middle notch of the M/L band, whereas the S band for the 42mm feels a bit too small (not enough excess band to tuck in) while on the M/L size the second notch from the left feels a bit too tight for me since I like to wear my watches a little on the looser side, while the third notch feels just a bit too loose.
Prior to the Apple Watch, I did have a standard Pebble smartwatch for the better part of the year and with the lugs, the screen was even bigger than the 42mm AW. So for me, the 42mm is totally the right one for me and while some people would say it looks big or comical on my wrist, I think it looks just fine and I love it. I wouldn't go back to the 38mm but I also wouldn't want to go any bigger either.