Great coffee in Union Square area? [San Francisco]
This topic seems to come up monthly.
Add Farm Table and Sugar Cafe.
I tend to visit Coffee Bar most often when in the area, but they're not about ambiance.
La Boulangerie locations are convenient, and passable, as a preferable option to their parent company, Starbucks.
They're actually well designed, ambiance wise.
In terms of leaving the area, I think what you want is Sightglass.
Second to that, North Beach has some options, and Contraband or Saint Frank come to mind, but both are better for coffee than the ambiance.
In short, check our Farm Table, and Sightglass.
Good coffee near Union Square is thin on the ground.
Coffee Bar on Montgomery is M-F only and only has limited outdoor seating under an overhang (not very soothing!) but I like their coffee (Mr Espresso out of Oakland) plus they have excellent pastries from Starter (kouign amann and others). Here's the link to the Kearny location (haven't been) which is also M-F only http://www.coffeebarsf.com/kearny
Blue Bottle Mint Plaza is our go to for fine coffee beverages and ambiance nearish Union Square. Great people watching in the always very long lines. I like their breaky offerings and sometimes there are food trucks in the plaza. http://www.bluebottlecoffee.com/cafes/mint-plaza
Coffee Cultures might work for you too, again M-F only but it has some seating indoors as well as out. Coffee is not locally roasted if that matters to you (Counter Cultures, Marietta GA). I've only had a mocha to go from there but it was tasty and the pastries were edible: http://coffee-cultures.com/
Coffee Bar has great coffee. There's one on Montgomery and another one on Kearny near Pine - both are northeast of Union Square. However they aren't sit-down places.
Cafe de la Presse has great ambiance. Nespresso cafe is also nice, if you like that kind of coffee (from Nespresso machines).