I'll play this game, even though my opinion probably won't impact your life at all. Disclaimer: I'm a GS PGY-1, so a lot of this information if from my limited access to various specialties.
I think it matters much more about the individual. I've seen a Neurologist work 8-4p in MS specialty clinics, and I've seen a Neurologist take q2 call as a stroke service staff. That guy looked haggard AF. I've seen pediatricians average 25 hr/wk and I've seen them average 60 hr/wk. I met one rural general surgeon who took Q1 call (crazy person) and I've met at least one surgeon who took no call (probably <3 yrs left in his/her career). It seems like the work is out there if you want more hours.
General specialty cultures for "relaxed" hours? Ophtho, psych, path, occ med, derm seem to have that culture. I am told by the EM folks that I work with that their hours can be nice if you're not at an underfunded county hospital (or "shop" as they say) and have access to scribes. General pediatricians seem to work relatively few hours, possibly due to the availability of Mommy/Daddy tracks (<1.0 full time equivalent, so you earn less too). Some medicine/peds subspecialties can have good hours, i.e. Rhuem, nephrology, endocrine, GI if in the right set-up.
Pholston brought up the medscape report (big fan of the mighty Pholston btw), I believe he was referring to the survey on hours worked per specialty. I would be hesitant to put much stock in self reported data of that type. I've seen firsthand how people overestimate the hours they work, and I'm not convinced that it's a systematic error evenly distributed across specialties that washes out.
There are extremes in everything. When you do a study you don't base your outcome on those extremes but on the medians. If you want a cush lifestyle look at the median hours for different specialties.