I just love the idea of helping infertile couples conceive. And along that same frame of mind, helping high-risk pregnancy patients have healthy babies (as healthy as possible, anyway). The pay is supposed to be excellent for both, and I'm pretty sure at least REI has a much more manageable lifestyle than general Ob/Gyn, but I think I'd really miss the ability to do regular old deliveries after choosing that specialty. It's my understanding that REIs refer the patient back to their regular Ob/Gyn (and/or an MFM, depending on the reason for infertility, I imagine) after they are pregnant, and MFMs probably do C-sections more than anything else.
And yeah, I also don't think I want to do a 3-year fellowship after a 4-year residency. I'll be 26 (almost 27) when I matriculate if I get in this coming cycle. Of course, it's only one more year than it would take to become a neonatologist.
Who the hell knows? Not me, apparently.