I can't say I really liked Deep Space Nine. I don't even remember the continuing story line. I guess I never really thought the characters were that interesting. To me, TNG was the most interesting. I thought there was excellent character development and good stories lines.Most series have gone to continuing story lines. If they had to depend on the quality of each episode to keep audiences returning, most of them would be lucky to last a session.
You know what, I kind of take an opposite view. I think "episodic" story telling in TV was a detriment.
Let's take Star Trek. You had "City on the Edge of Forever", where Kirk was willing to let the whole of history become undone to save the life of the woman he loved, but in the end, let's her get run over by a truck to correct the timeline. This was kind of a profound thing.
And it never gets mentioned again.
That's why I think the best Trek was actually Deep Space Nine. It had this great story arc that unfolded over seven seasons. Things happened that changed characters over the course of the series and we saw that change.