"That coffee shop's tea is the best."
Replying as a natibe speaker, if you add 是, 的 is as well required. This issue is too deep for new learners, since sentence structure is involved. Chinese had its own set of sentence structures which is seldom mentioned nowadays, and I'm not capable enough to tanslate it to English, so just consider it a conventional usage.
I know that 家 is also a qualifier for a business. I haven't mastered when they are required. I believe if you just say 'shop', you do not need the classifier. If you say what kind of shop ('phone store' for example) you may need the classifier. A native Chinese speaker could provide clarification.