We did two tours with the Sinh Tourist: 3 day, 2-night Ha Long Bay trip and a 3 day, 2 day, 3-night Sapa trekking trip. Confusingly, we found varying results with each.
3 day, 2-night Ha Long Bay:
Wonderful. Our tour guide was excellent, and provided a great history of Hanoi as well as answered any questions we had about present Hanoi. They took care of everything from transportation back and forth from Hanoi to Ha Long Bay, big seafood meals on the boat, and activities such as beaching, swimming, and kayaking. We were on the "Golden Lotus" junk the first night (smaller, older vessel), and transferred to a larger, newer junk (hilariously also named the "Golden Lotus") for the second night. If you are inbetween picking the 3 day, 2-night trip or the 2 day, 1-night trip I would HIGHLY recommend the 3 day, 2-night trip. The pace of the trip is much more relaxed, and on the second day you go to quieter areas of the bay where less boat frequent... also keep in mind that it takes 4-5 hours to go back and forth between Ha Long Bay to Hanoi each way!
2 day, 3-night Trekking Sapa:
Our guides for this trip were much more hands-off than any other tour I've been on. We were basically dropped off at the train station with an envelope of tickets and vague instructions about where to go and who to expect. We slept very little on the overnight train (the train would stop and go multiple times during the night to let opposite-direction trains pass), and were taken on a 4-5 hour moderately strenuous trek during the first weary hours of our arrival. Our Sinh Tourist guide did not speak much English, and therefore did not elaborate much about the Hmong culture or answer any questions we had. He was almost always about 100 feet in front of the rest of the group. Most of the information we obtained was from speaking Vietnamese directly with a couple of Hmong women who tagged along with our group. After 3.5 hours of trekking in the hot sun we were brought to Lao Chai for "lunch," which was the biggest tourist trap we had during the entire trip -- the food was poor and expensive (prices were unlisted, when we inquired we found out that "everything" on the menu was 80,000 dong), and it was difficult to eat with Hmong women and children pleading with you to buy their bracelets and coin purses with each spoonful you took. On the second day, we received a new guide for our trek down to Cat Cat and the waterfalls... and again, we were led to a tourist trap. At the very bottom of the valley, we were told that we could either trek back up the way we came (which they said would take at least an hour), or purchase a motorbike ride from many of the xe om vendors. Our group is in our 20s and decided to trek up (more on the theory of principle against tourist traps than to our own strength), which only took about 40 minutes. Many other folks chose motorbike rides though.
In hindsight, we would have much rather planned the Sapa trip ourselves and hired a Hmong guide (from Sapa Sisters, or one of the many other Hmong guide organizations in Sapa) once we arrived there. We would have then a) known exactly where we were going and what to expect and b) gotten a much richer cultural experience and historical context.