"That coffee shop's tea is the best."
As a Chinese, we may say “那家咖啡馆的茶是最好的。” Without “是, it sounds a little bit wired.
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.
Yes, as far as Standard Putonghua is concerned. Certain dialects may omit it, however.
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.
I could be wrong but i thought 店 is for a very small shop but 馆 is for a larger store. So guan might be better for a cafe where people can sit, whereas dian might be for a very small kiosk, tiny shop, and not a typical size for a coffee place?
I agree that 馆 is used for larger structures. I have seen 店 used for restaurants and hotels, in older Chinese movies. That is why I am curious.
Thank you for answering.
I cannot see that a coffee shop's(café)sell tea and it is the top of this county or city or region...