The Mezzaluna (Half moon) is unquestionably the best tool there is for
chopping herbs. When you chop with a prep knife, the strokes mostly
bruise rather than cut, because the blade will be square against the
board in only one spot. With the Mezzaluna, every rolling stroke cuts
cleanly through - you get a much nicer looking pile of chopped herbs
and you get it a lot more quickly.
Food processors? I've found that by time they get herbs chopped evenly, they're chopped too fine, almost to mush.
And those plunger choppers? It is to laugh!
This knife is known mainly in the Mediterranean region, where large quantities of chopped herbs are used. The herbs are piled on the cutting board and the knife is rocked smoothly back and forth and rotated slightly with each stroke. This motion takes a little getting used to, but very little, and is well worth the effort.
The photo specimen was a very low cost item - I bought cheap because I wasn't sure I would find it useful. Stupid me. The blade is 6-3/4 inches tip to tip, and badly needed sharpening. I intend to get one more like 7-1/2 to 8 inches across. There are also versions that have a single bridge handle you grasp in the center, like an Inuit Ulu, and versions with more than one blade for even faster cutting. The Mezzaluna is a clumsy device for general vegetable cutting, but might be useful to chop some coarsely chopped vegetables finer.
More on Knives.