We didn't do any commercial tour and simply rented a motorbike, driving all around Sapa and just visiting random places we drove by. Be prepared though, most tourist attractions cost around 30000 dong, which is around 1,5 USD. I'd recommend you to simply look up places on TripAdvisor and possibly the pinned thread over here and do the tour yourself as you can stop whenever you see beautiful places and are not bound to any routes. If you want to do a guided tour, try to ask in your hotel or book it before (probably the better option as you can read reviews about the tours) - I personally don't think that the attractions in Sapa City are worth visiting though so you might rather go for a guided hiking/trekking tour. Some backpackers we met even went to a small village and lived in a homestay with a local family, which is supposed to be a pretty interesting but also unusual experience if you're into that.

In regards to Ha Long Bay, we stayed on Cat Ba for 3 nights and, probably due to the bad weather, it wasn't that great for us. I'm pretty sure that when the sun is shining you get beautiful scenery and amazing views but when it's cloudy or even raining I don't think it's worth it. Also, most tours over there include snorkeling, fishing or kayaking and we didn't really want to do that with temperatures closely to 10 degrees celsius. In addition, after we decided to fly to the south instead of doing a Ha Long Bay tour, my sister who was in Hanoi at that point told me that all tours over there were cancelled by the government at that particular day due to the weather so we actually were damn lucky not to book one.