EM - variety, fast pace, focus on diagnosis, little to no treatment stuff, no ongoing pt care responsibilities, shift work. Almost chose it, actually. However, disliked drug seekers, and non-emergencies/chronic probs that were just an issue of poor access to primary care. After a while, got tired of the parade of patients demanding something from me and me not being able to fix them.
IM - emphasis on underlying mechanisms, evidence-based approach. But, and this is a big one, I do NOT like dealing with chronic problems, especially treatment of them. It feels futile to me. I like to fix things and you do NOT get that in IM, outside some ID stuff. I also don't really buy into the mentality of IM. There are some really crazy and masochistic aspects of it, that only first-hand experience will teach you whether you're cut out for or not.
Surgery - feeling of "fixing things", actually making people better, almost chose general surgery for that reason. Liked the variety at the time as everything was new to me, but I have a feeling that after a while hernia repairs would become pretty boring. Hours are a huge drawback...even attendings still work 60+ hrs a week.
Urology - seriously considered for a while - somewhat better hrs than general, plus it includes warm fuzzy counseling stuff that I do kinda like. Also felt a personality match with the particular group I was working with. Liked the plastics procedures (which also led me to consider plastics). But, just not cerebral enough for me, mostly just plumbing.
OB/GYN - Delivering babies is just plain cool, so for about a week I was sold on OB...except when they are crack babies. Gets depressing after a while. The hours in OB speak for themselves, as well as the malpractice. Looking in vaginas all day is not my favorite thing to do. Most importantly, the attitudes and personalities I encountered in this field were malignant, stressed, power-tripping. *shudder* Bad memories.
Radiology - Very cool, technical, opportunities to do procedures and talk to clinicians, clinically relevant, but without ongoing pt care responsibilities. Loved the personalities. But I have 2 radiologist friends who actually work their butts off, contrary to popular belief, and are bored with what they are doing. That's the main reason I stayed away.
Peds - Kids are fun. When giving out Spiderman stickers makes your patient's day, life is good. On the other hand, you trade in mental challenge. Most outpt peds is well child checks, runny noses, etc., and placating worried parents, every one of whom thinks their Billy or Bobby is a little king. Did enjoy working at a clinic for unisured Hispanics, really enjoyed the family dynamics and interactions there, but have a feeling it wouldn't pay very well as a career.
Anesthesia - just the right amt of pt contact, get the warm and fuzzy stuff making patients feel less nervous before surgery, no ongoing pt care responsibilities, get to be in OR environment which I like, shift work, cool personalities. But I don't really like pharmacology at all.
Psych - Actually a lot of potential to fix people, especially inpatient psych. Psych pts are much more rewarding to work with in a psych setting, rather than as a disruption to your day in IM or surgery. Of course, some patients are already so far gone, and have suffered so many horrible things in their childhoods that they aren't fixable and that's depressing. Outpt psych was a total downer. Try seeing 10 pts in a day ALL of whom are depressed and want to talk about it. *shudder*...not sure my own mental health could survive.