I always figured seamed stockings are used for a very specific look, and formal wasn't the one; I think they're used more for lingerie and fetish type wear, or the type of clothing style that might go for that look (i.e. goth, punk, etc.), or possibly a "vintage" look (i.e. back when they actually wore seamed stockings). I wouldn't personally opt for seamed stockings unless that was the message I wanted to send.
As far as whether to wear regular stockings or "holdups" (are those thigh-highs?), I think it depends on what's comfortable for you. I, for example, hate regular stockings because they're not comfortable--too tight at the waist, usually not long enough so I have to really pull them tight at my toes to get them to reach my waist, and they tend to ride down. However, I also don't like thigh-highs because they won't stay up (though I'd opt for thigh-highs and add elastic to hold them up any day). Whichever you feel won't make you feel the need to pull awkward maneuverings to keep them up is probably your best bet. <img src="/images/graemlins/smile.gif" alt="" />
