Well I've got to admit I just picked a random episode in the end, there was a list of about ten that I was trying to pick from so it's impossible to say definitively what my favourite is. I ended up voting for Red Dress, mainly because after only half-watching the pilot, this was the episode which got me completely hooked. Also, it's kind of characteristic of a type of season one episode that we no longer see. Given that they're all grown up now, Lois can't use the same type of methods to punish them as she does on this occasion. It's very much kids vs Lois, whereas now they'd all be off doing their own thing, and are less likely to act as a unit like this.
I have to say though, if you're one of those fans whose come late to the show, and may not have seen the season one episodes, buy the dvd now! It's easily the best dvd i have in my collection, and i've got some quality comedy dvds if i say so myself
! I know people go on about this, but every episode from this season is an absolute, must see, classic. They're the type of thing that you can watch over and over and still find funny, so if i could have voted for the whole season instead of one episode i would have, even though that totally defeats the object of the poll.