Starbucks is crap. Dunkin is decent, and by Dunkin I'm referring to buying the beans/grounds yourself and brewing. Buying it from the store or from a Hess station or something is not even remotely the same.
If you absolutely have to get coffee on the go, outside of whatever your indie coffee shop of choice is, the place to stop is at a Pilot Travel Center, or maybe a TA (Travel America travel center). Loves or Petros are ok but less dependable on consistency. Just about anything else you get on the go is going to be coffee-ish flavored piss water. Or if it's Starbucks, it's just burnt dreg tasting.