Hmm...a dumb ecchi comedy vs a fascinating (if not entirely successful) deconstruction of a dumb ecchi comedy..;.
I'll go with Chobits.
Chobits by far.
My vote goes to Chobits.
Heaven's Lost Property all the way i enjoyed it and laughed more watching this series then i did chobits.
Although the animation and characters are a whole of a hell lot sexier in HLP, I gotta vote Chobits as the better overall series for its story/plot lol.
While I don't hate 'dumb ecchi comedies' as it's been put (in fact, some of those are downright hilarious), I'll have to go with Chobits on this one as well.