Which one do you like better

Neither. They are both clichés.

A benchmark is a measure.

A landmark is an outstanding feature.

Both expressions are cliches, but they are chiches with different meanings.

Cliches or not, can you clarify what you are trying to say? If you are measuring something then benchmark is fine, you don't need event on the end.

If you are using landmark, event on the end is okay.

"Benchmark" has a specific meaning in UK English. Benchmarks are various marks made by the Ordnance Survey (the government agency responsible for providing mapping and other survey information) to record height.

Here is a benchmark cut into a stone wall. The benchmark is the horizontal line and indicates height above sea level.



I understand that in US English, benchmarking is a sport in which individuals or teams of participants go out and find benchmarks (also known as geodetic control points).

A "benchmark event" might be when your child took his first step. It is a measuring point from which all other things are measured (like when he started crawling, then took the steps, then starts running)

A landmark event is one event that is special and is noted at that time and place, like the landing on the moon.

I agree, they are equally superlative.