Season 2 is amazing, my favorite season of DS9, far superior to seasons 3 and 6 in my view. Start with The Emissary and watch the series from start to finish.
Season 2 is also my favorite. It's excellent and it's easily the show's most diverse and risk-taking season, with so much variety in the kinds of stories in tells. The later seasons, while excellent, constricted the show's universe a bit and so much focus was put on the Dominion War that the funky, more experimental vibe was lost a bit.
That said, Season One definitely has a few stinkers you could totally skip without missing anything and even season 2 has a handful of duds.
I'd watch about 60% of season 1 and 85% of season 2 and then watch everything else (well, you can definitely skip some of the Ferengi episodes and a few other clunkers here and there.)