To start with, how many days ?
A package is the worst you can take. You are bused from one place to another, group hotels, so-so to bad group food, etc. Fly Hanoi, 2 days up there, 2-days cruise Halong Bay with local agency, then the magnificent northern mountains in 4-6 days, then day train Hanoi-Ninh Binh, 2 days Ninh Binh/Tam Coc, then night Train Ninh Binh to Hue (2 days) then it depends on how many days you have total
How can anyone tell the poster what they will love without knowing anything about them? They may hate cities, or countryside, and may prefer booking a tour. Thousands of people visit every year on tours.
Tell us what you like to do, your budget ie low, medium, high, how long you have and why you picked Vietnam. Then people can suggest what you might enjoy, but you will need to do your own research. If you do decide on a tour, you will be moved about quickly but that might be what you want?
And when? Weather changes which area is better.Edited: 23 September 2018, 11:59
Tell us more about what you like. In the north, if you like remote areas , go to Pu Luong Nature Reserve and as mentioned before, contact Eco Travel Go Green, they do very nice tours there that you can combine with ninh binh and Halong Bay.