<p>doubles are the most preferred at UCLA, and also in the shortest supply. if i had been in a double this year, i’d do it again next year. if you and your roomie are compatible, then it works out quite nicely. you get (depending on the school/dorm) quite a bit of space, and you aren’t isolated, even if you’re the type that always stays in the room.
triples here are rooms meant for two people but with three in them. unlike my friend’s triple at berkeley, which is effing huge! some people have no complaints, some have tons. as they say, two’s company, three’s a crowd. but there aren’t always three people in the room except at nights (sometimes not even then) so it’s usually like a double, only with extra furniture and a revolving roommate 
i am always slightly envious of those who have a choice of what they want their freshman year, because 98% of us (or so it seems) were assigned triples. which i would not have chosen, but it’s kind of like having the “college experience” foisted on you, but twice. which i think would have been accomplished quite well in a double. or in a res hall, if you want the TRUE college experience, communal bathrooms and all! xD</p>
<p>ups and downs of a triple room, from my experience:
(positive) two chances to get roommates you’ll really click with, more built-in social opportunities, two built-in acquaintances (if not friends), little/no danger of isolation, two new people to expand your ideas about what college life is like, two people to compare your experiences with, guaranteed necessity in changing one or more of your habits (good for the ol’ life skills set), you learn how to compromise, and you’re more likely to share classes with one or both roommates.
(negatives) two chances to get roommates you’ll be at odds with, lack of space, less privacy than you may be used to, two people’s living habits to get used to instead of one, conflict over bathroom time (if in-room), more chances for conflict in general, more potential for drama, ability for two roommates to click and one to feel left out, unevenly divided furniture/closet space that can lead to conflict… well sum it up to say there’s more potential for conflict.
some people DO choose triples, because they’re cheaper, and/or they have two good friends they’re compatible with as roomies. if you didn’t choose a triple, or don’t know your roommates, then you just need to be assertive. same goes for doubles, but issues can get magnified in a triple.
if you want my true opinions… suffice it to say that next year, i’m living by myself. then again i am an only kid so this year has been interesting! but if i’d had a choice as an incoming frosh, i would have chosen a double. a happy medium between the two. and a lot of people just plain don’t like singles.
my (quick) take on singles: go out and socialize when you want to… and come back to your own room without any roommate conflicts when you’re done! (if you have roommate conflicts in a single… you need a room with a nice flat couch )</p>