No I am not pitting each cast of girls against each other to see who would win in a fight, but rather I want to talk about the ways in which these three shows differ beyond a superficial level. You’ll sometimes hear people say that Kyoto Animation’s about is all the same, and I will agree with them as far as saying that they know their audience, i.e. otaku, but when you actually watch these shows you will most likely get a different vibe from each one.
I won’t be discussing the Key adaptations because that’s another beast entirely.
With Haruhi, you’ll notice an air of mystery that permeates the show due to the supernatural aspects of it. Sometimes it’s more obvious, but other times simple actions can imply greater things, and it gives a certain sense of intrigue to the series. It’s still all about a bunch of high school kids hanging out and doing dumb things, but even the dumb things are given a sort of significance as a result of the setting. You can always feel that Haruhi is moving somewhere (right to what the light novels have already spoken about!).
Lucky Star is not just otaku pandering, it is active otaku pandering, and that’s also what makes the show enjoyable. More than either of the other two shows, Lucky Star asks if you’re an otaku, then asks one more time just to make sure, and then high fives you because you watch a lot of anime. In fact, Lucky Star probably does this more than any other show, but don’t think that all the humor is in-jokes with no setup; all I’m saying is that the show rewards otaku.
K-On! meanwhile does away with the pretenses of the other two and is simply about what it advertises: cute girls playing instruments and not being too obsessive about it. There are no undercurrents, no subtle themes at work here. At the same time, I wouldn’t call K-On a shallow anime, as the humor derives from the characters’ personalities very heavily, possibly more than Haruhi or Lucky Star.
All three shows feature groups of girls having fun, but the effects they have on the viewers will vary tremendously due to the inherent differences in each show. If you hate one show you might not necessarily hate the others, and if you do like all theree, there’s a good chance you’ll be liking them for different reasons.