Here's a house where the gutters have become planters!
Cleaning gutters (and anything else done on ladders) is a major cause of death among men of a certain age. It also results in cut hands and a messy yard below. I have found that Gutter Helmets work best. Designed like an air foil (wing or sail) debris, except for some pine needles, falls over the gutter and water, because of its high cohesion (hydrogen bonds) sticks onto the guard and just wraps around into the gutter: except at the seams and with a really heavy downpour.
Another problem was at my mother-in-law's house where a lot of moss had gathered on the roof and actually between the gap in the guards: this led to flooding of the basement because a large portion of the roof drained onto this section. So clearing out six inches of the gap solved the problem.
The company will come and prepare for a new roof when you get new shingles, so they really will last forever. Click on top image for link.
Screens and foam just get the gutters clogged worse with smaller debris.
Here is a flat roof solution with no gutters in Skyland. Note the normal side flashing but with serious fluted metal below with the drip edge far over the soffit.
My Gutter Helmets started to drip over the seams. The problem was debris covered the attachments, so you just clear them with a finger or a spray of water/