I don't think you can include DS9 with TOS and TNG as far as morality. Star Trek and TNG were both very idealistic, "Good guys in white hats." DS9, especially later in the series, was much more realistic in that the characters were highly flawed and made very gray-area decisions (especially Garak, who was one of the most fun to watch. Sisko was also capable of doing some underhanded things that neither Kirk nor Picard would have even considered). However I enjoyed all three shows (until Paramount proceeded to photon torpedo the series' credibility with Voyager, Enterprise, Insurrection, Nemesis and now the "Reimagined" original crew. The guy who played the Doom Guy has NO business cast as McCoy!)
I don't watch the new BSG at all because they ripped the heart and soul out of the original and changed things that had neither need NOR reason to be changed.