depend on your taste. If you want Vietnamese hard coffee you can go to Trung Nguyen Legend or highland coffee "ca phe sua da". There are Starbuck there.
I'm highly recommend Giang Cafe, in which you can enjoy egg coffee, one of speciality drinking in Hanoi. If you want to discover a recycle coffee shop, you can come to Hidden Gem Coffee in Hang Tre street. In here you can taste cafe, juice, ... which are poured into old wine bottle, you can sit on chair recycle from old car tires.
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I remenber one Giand cafe in last trip for Ha Noi, Untill driver in car of 8rental, the GPS tell me one address very close in down town and I can say is very good cafe.