I love all of them,but some of them are really sad, so I don't re~watch them eg. Ep. 582, poor guy :'(
If I HAD to choose, then I would say, the Valentine's Day one when Makoto (Sonoko's BF) gets really jealous of himself, of course he didn't know he was the "Lucky" guy.
Other than that, all the episodes are AMAZIN!!!!!
I can't believe I watched all the episodes twice within 3 months (600 or so)
I should stop my rant now