Level term
The sum assured stays the same across a fixed term. Straightforward and predictable, it suits a defined lump-sum need — but a fixed figure loses real value to inflation over twenty or thirty years.
Decreasing term
Cover reduces broadly in line with a repayment mortgage, which usually makes it cheaper. It matches a falling debt well and matches a family's wider needs less well, since those do not conveniently reduce each year.
Whole of life
Intended to remain in place for life rather than for a term. It costs more because a claim is expected at some point, and it is most often considered where a liability does not disappear with age.
Reviewable plans can become materially more expensive at review, so the structure matters as much as the initial premium.
Sources and further reading