Lycra seems to be the most comfortable and practical (I'm also worried about catching baggy shorts on my seat), though it seems baggies are more "fashionable" for mountain biking these days. Wear whatever works for you!

XC rider

(p.s., Just don't do what I did and roll down your lycras for a quick stop behind the bushes without looking, and end up with a load of burrs inside your pants -- OUCH! I swear there are still some lurking there to this day.)