Ds9, TNG, Voyager, enterprise, ToS would be my preference but I 100% loved ds9 for its varied and unique characters and storylines, not many trek shows did the time travel part right, sure picard met kirk upon taking on the mantle, but Captain sisko and his crew met Captain kirk literally on his enterprise.
Not even seen the discovery yet but hear they are making another discovery spin off series for that one too.
Its such a shame trek films are probably canned for now but the old formula of bigger and better baddie then last outing was getting so old and boring and I am surprised no writers/producers noticed that trend, with CGI and technology I would have preferred a mish mash time travel film with all shows and cast popping up or have reality shattering alien species and bring in a giant epic war blast combining the kelvin universe and original universe cast.