I use the cheap steel black coated ones from Home Depot with 1/4 inch mesh. All the trees in my house are oaks, and t h eyes work just fine. Only roof shingle granules land on the bottom of the gutters and do little to restrict the flow of water. This would not work with pine needles.
I've tried most gutter guard systems and they usually work for a few seasons, before they start clogging up in their own way. I've never paid anyone to install one of those systems; because I'm too cheap and don't really believe them to begin with. I've installed the wire mesh ones from home depot. That took 3 years to clog up, so I removed it. It's just simpler to just move a step ladder to the down spout, reach-in and remove the little beaver dam. The small branches that caused the clog in the first place; floats and spills out over the side of my gutters. My gutters are large and deep enough to flush all the dry leaf materials through the down spout. I only have to do that once a year, when I see my gutters overflowing. Usually during the first heavy rains. And I get to invest that $15K instead.......
