Any idea what you want to do with pathology post-residency? I think that would be the biggest determinant as to whether you would benefit from AP only.
Here is some thoughts:
1) Most AP-only programs are academically geared, so you would be expected/trained to set yourself up for an academic career and research. For example, a few of the high powered research programs that I interviewed at (Brigham, Pitt, and Hopkins) all had folks that *strongly* suggested that I lean toward AP only based on my interest in occupational lung diseases. In fact, they seemed to have my academic life planned including what research lab I could work out of.
2) If you want to be a generalist (particularly community), do both. You are more employable, as most lab groups want to have a bit of cross-coverage amidst their pathologists. In fact this was the advice given to me by a "famous" AP-trained pathologist (yup, the same one who wrote THE book on lung path, and now director of surg. path for my institution... woo hoo! PM me for more info). Even she said she regretted not being CP trained, and that she received less job opportunities than her AP/CP colleagues. Note: She worked for a community hospital as a generalist / lung consultant prior to her employment by my home institution--a rather unusual situation for such an academic powerhouse.
3) If you are contemplating forensics, you probably could get away with either AP or AP/CP. Forensics tends to have a high drop-out rate, so to speak, so if I end up doing it, I will get AP/CP certified with probably a surg path fellowship along with a forensics fellowship. Yup, I like to keep my options open.
4) Obviously, no AP only if you have an interest in lab medicine. This does include Hemepath, though, so if you like bone marrows and flows, think CP.
I honestly do not know which is more competitive. I think that less people are interested in pursuing AP or CP, than a combined program. I don't think that AP fellowships would look down on AP-only training. Eras DOES ask you to specify AP/CP versus AP, or CP only in many cases (depends on the hospital.) There is more AP/CP positions than one or the other. I think that there is some flexibility in most programs about whether you choose to pursue one or the other, and how many people they will take for each. Hope this answered some of your questions...
Well, I'm sure there is other good advice out there...