I'll be glad to say that both are really wierd. I actually went to a convention or two in my youth and when a guy like me, who's waaay up there on the nerd scale starts to feel ashamed to be somewhere you know it's bad. The people are always nice enough, it just seems that they are oblivious to how foolish they look, and I don't mean just their appearance but rather their behavior (being waaay to serious about their costume/persona or worse yet thinking that by doing a really poor imitation of the character they are being cool).
All of that being said, trekkies are worse but it really doesn't have anything to do with their preferance, rather it's all in the costumes. 90% of Star Trek costumes involve spandex, a material that nobody looks good in unless they are in really good physical condition. Most Star Wars costumes, on the other hand make use of flowing robes or capes. Those tend to look okay on anyone. Also most star wars characters are human or wear a plastic mask, while most star trek characters involve prosthetics (that most people can't apply properly I might add). So by default the average star trek fan looks dorkier than the average star wars fan when in costume. It's a fact.
All of THAT being said, Star Trek is still the supeiror franchise and thus more worthy of extreme dedication. After all, star trek has given us 5 television series, all of which were pretty good to fantastic. Star Trek has also given us several movies most of which were really good with a stinker or two mixed in. Star Wars on the other hand has basically given us 6 films, three of which being so horrible that most fans completely ignore their existance. So look at it this way, at least they are obsessing over something worthwhile as opposed to something stupid (ie football or nascar).