Starbucks -- or "Charbucks," as its critics like to call it -- serves really horrible and overpriced coffee drinks, IMO. I am a bit of a coffee geek, so I'm probably more discerning than the average consumer, but nonetheless I find the quality in beans and technique lacking, especially when you're talking espresso or coffee made with a french press.
Simply put, Starbucks really has become the McDonald's of the coffee world.
No experience with Tully's, but Peets is by far bettter in overall quality, employee training and general customer service. Peets is a chain, but it's simply a smaller company that can buy and roast beans in smaller, more selective quantities. Peets also seems to just care more about the coffee, and less so abouut the pseuudo coffee drinks (Frappucino in a can) or accessories sales.
Visit Peets and decide for yourself.