Bistro Don Giovanni is hands down my favorite place to eat in Napa. It's just North (?) of downtown Napa headed toward Yountville. The hospitality there is as lovely as the food. Even without reservations, they've graciously found a place for me at the bar or set up another table.
Can't help with Santa Rosa. For Napa Valley I like Jole and Solage in Calistoga, Bouchon and Ad Hoc in Yountville, Bistro Giovanni at the outskirts of Napa. Cindy's in St. Helena is also very reliable.