Can't say that any guard is going to be the easiest, especially if your shingles are sealed down.
The gutter guards that I like are sold at Lowes and Menards. They are 4 ft long plastic guard with round holes. The holes are covered with window screen. I don't have to worry about maple spinners getting stuck in the guards like they do in most other guards.
I have taken sheet metal screws and attached them to the top of the gutter if I can't get it to snap and stay in place. I've also takens sissors and trimmed them to fit.