They're both incredibly sexy and feminine. And I mean the blow-your-load-(and your mind)-on-the-spot kind of sexy. The only difference is that black pantyhose, and black tights even more so, add an extra touch of warmth and femininity (note that I'm not equating femininity with sexiness here) to any outfit. But honestly, if you wear either, you'll automatically place yourself in the top 0.1% of American women when it comes to classiness, sexiness, and femininity. And, as an added bonus, if you wear either, but especially tan pantyhose, men will think you're the perfect marriage and housewife material. Crazy how pantyhose has the ability to make you look ultra-sexy and traditional and conservative at the same time! On a side note, I've never acquired a taste for cuban heels. To me, they look dirty and smelly, but not in a good way, and especially on tan stockings, and something's visually off with the way they look, at least to my eyes. I think they in a way ruin the sex appeal. Back seams, on the other hand, are great, but that's really just too much sexiness that's best reserved for a few rare occasions. Also, some guys on here are trying to steer you toward stockings instead of pantyhose. My take on that is, stockings are almost (a very close runner up) as good as pantyhose, but they only make sense to wear if you want to add a touch of timeless, vintage sexiness to your style. If that's you, then go for it, and you'll have a lot of fun with them. If not, I don't see the point, unless you just want to wear them to look sexy, which they abundantly are, but then why not get the same result by wearing pantyhose? If you do ever wear some stockings for a change of pace, enjoy the process by also buying some classy, high-quality garter belts.
A bonus tip: If you have a normal (average) figure, try this for a cute sexy-around-the-house look: Black classic pumps (closed, shiny, not too pointy; small peeptoes work nicely as well) with black, reinforced toe pantyhose (the Hanes Silk Reflections brand is amazing for the price) and black leggings (try the Express Sexy Leggings; they're very soft) over them. The ultimate in warmth and femininity. Or, for an even more casual look and something you can wear everywhere, you can replace the leggings with a pair of medium blue jeans that fit you like the leggings (has to be snug around the ankles). Do that, and you won't be able to shake men off.