Stressors in L&D are of an immediate, acute nature...Impending delivery, dealing with newborn recussitation, communication with pts, families, & physicians (sometimes firmly or very assertive), poor outcomes, & thinking on your feet (many times while running down the hall). Although this is stressful, it's important to remember it is very temporary...the light is at the end of the tunnel. You do need to have a little adrenaline junkie in you to appreciate it, though. Also, as deerhavern stated, there is noooo way to schedule anything in L&D. Every day is different--a vast difference from sched med passess and assessment times on Med/Surg.
On med/surg, the patient load is greater-- more meds, treatments, more frequent head-to-toe physical assessments. Time constraints are a big stressor. And that patient who is on the light every 5 mins may come to visit you frequently for years and years. But there is not the daily influx of emergent situations (generally).
I've done both, and really love OB! I did not Med/Surg nursing--just not my cup of tea. As far as stress, just ask yourself WHAT stresses YOU out. If you don't have a bit of the adrenaline junkie lurking around somewhere, OB may not be right for you. If so, give it a whirl!!!
Oh....one big bonus on L&D. You're not usually ever around any sick people! I love it!!!! No more worrying about what crud I'm bringing home to my kids!
Good luck on whatever you decide!!!