It annoys me when people assume that someone is not sincerely interested in a field or interested for the "right reasons" just because the person is interested in 2 fields that don't have a ton in common. Many people enjoy multiple rotations, even if they have nothing in common. It's not like there is one field that each person is destined to do.
On that note, who is to say what the right reasons are for pursuing a specialty. Obviously we all know that on residency interviews there are certain reasons you should give for your specialty choice and others that should stay out of it (i.e. easy lifestyle, money, prestige, etc). However, I think everyone who cares about things like earnings/lifestyle should factor these things into his or her career decision. As long as you dedicate yourself to your chosen specialty and do the best job that you can do, who cares if you went into it partially for the money or the prestige or the lifestyle.
Now to answer the OP's question:
I don't know a ton about the pluses or minuses of ortho since I never really considered this as a career option, so I'll stick to derm.
POSITIVES OF DERM
1. Continuity of patient relationships
2. Healthy patients
3. Make a real difference in happiness/self esteem
4. Low stress, few emergencies
5. Call is very light, good lifestyle
6. $$$$$
7. Interesting diseases, lots of variety (from acne to cutaneous manifestations of connective tissue disease)
8. Combination of medicine, path, surgical procedures
9. Visual diagnosis- don't have to take long histories
10. Very little inpatient work!
NEGATIVES OF DERM
1. Some of the diseases are pretty gross
2. Some disrespect from other physicians who think derm isn't "real medicine"
3. Hardest specialty to get into
4. Most procedures are pretty small (negative if you're into more gen surg type stuff)
5. Boards are annoying- have to learn lots of useless stuff about very rare diseases (I hate genetic syndromes)
I was being a bit facetious when I asked that question. It's clear that both are specialities and both do consults.
But this could be said for many fields -- derm vs ophtho, derm vs ent, derm vs...you get the point.
It sounds to me that the OP has no "real" reasons for wanting to pursue derm vs ortho as the two are vastly different specialties.
Some soul-searching and mentorship are in order. I'll let the derm residents take over from here.