score:4
Tet like Song Kran in Thailand (and I refer to the actual Song Kran not the tourist fork) is pretty much of a family holiday. People travel back to be with family during the holidays, so public transport likes buses, trains, etc are packed during the days leading up to Tet and the days afterwards.
But the Vietnamese tend to stay with family when they come home, so small town hotels are not usually over run. But that is not a guarantee, as better off Vietnamese may prefer comfort of a hotel over the basic house of their parents, as well as those who might have foreign spouses not used to sleeping on floors.
A lot of tourists come during Tet to see the festivities in the big cities, so bigger tourist destinations will be packed.
Upvote:2
As Tom said, Tết is a family holiday, so most people would return to their hometown and stay in their houses, therefore hotels and guesthouses would be rather empty those days. In major cities like Ho Chi Minh city or Ha Noi it will be quite deserted and quiet unlike normal. However other touristy places like Đà Lạt, Nha Trang, Vũng Tàu... would be very crowded because some people don't want to squeeze themselves on the overly packed vehicles going home and choose to go "backwards" instead and visit their hometown another time, and finding a bed in those cities would be a pain