The ones with screeens and grates, etc, clog any way....stuff settles on top of them, etc.

The large opening allow small leaves and twigs in, which mesh and form dams, etc.

The only truly working solution is the Gutter Helmet.

Its solid on top, so no leaves can get in, no matter how small...the water follows a lamnar flow pattern over an over hanging lip....and particles in the water, dirt, leaves, etc...can't make the turn, and fall off, the water itself follows the lip back into the gutter.

I had several oaks, tulip, elms and maples which clogged every damn thing I tried....except the Gutter Helmet.

I had the house resided, and the guy accidentally trashed the gutters, and threw out the Helmets.....and replaced it with "Ones Just Like Them", same laminar flow principle, etc....but, they just don't work as well, and I had to go up on the roof and clear the friggin gutters again, after years of not having to...

So, that's the ONLY one that really works, despite a plethera of marketing claims by others...the Gutter Helmet.

Hope that helps.