Best Mexican/Latin resturant in Fairfield county area?
From the places you mentioned, it sounds as though the bar scene is as important as the food itself (I am a big fan of Brasitas, but find Rio to be generic Tex-Mex). I would suggest one of the Bodega Tacos in either Darien or Fairfield, or its older sibling Valencia Luncheria. All have excellent food along with creative cocktails and lively bars.
Some of my favorite Mexican restaurants - Tacos Mexico and Los Molcajetes in Norwalk, and Casa Villa in Stamford - have very authentic food but are much less of a night on the town.