Cafe de la Presse and Nob Hill Grille [San Francisco]
I haven't been to Nob Hill Grille. The couple of times I tried breakfast at Cafe de la Presse, it seemed underwhelming to me.
Depending on what you like for breakfast, and where you'll be staying, you could try La Boulange on Sutter Street (btwn Kearney & Grant).
Although it might be a bit far afield from Union Square/Chinatown, the Blue Bottle cafe at Mint Plaza, has a limited, but very tasty, breakfast menu--bonus: Blue Bottle Coffee.