I work at Tully's Coffee. We use Ghiradelli Chocolate syrup, which isn't the best chocolate in the world, but it is much better than Hershey's and commercial chocolates. Most places use powdered chocolate, which personally I hate. I drink Starbucks, Coffee Bean, Peets, etc. on my days off. I think each Mocha is different, some are grittier than others.
You might like the Intense Dark Mocha, which is made with dark chocolate Ghiradelli chips, it taste much creamier. Or maybe you just prefer the Very Sweet Hershey's chocolate.