I've tried several kinds, but none were satisfactory in the long term.
Our houses have been surrounded by maples and oaks, and the amount of stuff that filled the gutters, both Spring and Fall, was amazing. It either clogged or bypassed all the different gutter guards I had.
Assuming your house actually needs the gutters (see posts above), I used two cleaning techniques that worked. My gutters were only about nine feet off the ground, so I just walked around the house and cleaned them. Generally twice in the Spring and twice in the Fall.
One method was a long extension with a U-bend on the end that fit on my leaf blower. I could just direct that airflow into the gutter and blow the crap out of it.
The other method was the same, but a long wand with a U-bend that attached to my garden hose.
Both techniques actually worked, but there was a lot of nasty stuff blown out of the gutters while doing it. I had an old pair of coveralls and big hat I wore while doing it, to protect myself from the overspray.