Inpatient: I did MHT, really loved it. It was a great first rotation to have, because you do see a really wide variety of stuff, much of which is tested heavily on the shelf. I think going into it though having already done medicine may end up being a little more boring -- most of the patients there have minor problems and are out within a few days. Very few really, really sick children (which I liked, actually -- I enjoyed seeing the fast turnaround from problem to solution). Another positive element is that all the attendings there are really nice and really into teaching. There are no residents/interns, which I was initially worried about, but the attendings are super approachable, and in fact, never stressed out or cranky. Most of them have small children at home who they actually spend time with, and are very into creating a positive work/learning environment, and are generally laid back and aren't trying to put you through the wringer.
Outpatient: CHOP South Philly. This is often regarded as one of the best ones -- after a day or two, you take care of the entire patient encounter on your own, write the note, etc -- the attending will come in and check that the patient is fine etc, but you get a lot of autonomy and learn a lot. Again, everyone is super nice and mostly good at teaching. Speaking Spanish comes in handy here as well, as many families are Spanish speaking only.
Overall, you can't really go wrong w/ peds. Everyone's pretty nice, and I haven't really heard of anyone having a terrible experience.