It depends on what the aircraft are made out of. For the clear styrene ones, I hand-painted each one on my USS Enterprise build, and just took a great deal of care to keep the brush away from the canopies and coat that area with Future when done. It turned out fine, to my eye - but, you have to remember to put an "undercoat" of some dark gray color on the bottom of the aircraft, under the canopy area, to give it a bit of depth. I tried using some gold on the sides of the fuselage before painting the EA-6B Prowlers to simulate the gold tinting of those canopies, and it turned out OK in the right light:
For solid plastic canopies, I did a lot of experimenting and came up with a combination of Tamiya acrylic Smoke over Testors enamel Steel for the Jake canopies on my IJN Kimikawa Maru build:
But as Chris said, there is no one right answer. If gloss black looks good to you, then by all means go with that!