Though you might think all garlic powders are the same or at least interchangeable, you'd be surprised at the variation across brands. Different garlic powders exist in a rainbow of colors - from eggshell-white to gray-lilac - and possess textures from true powders to more iodized-salt-like grains. There are even discrepancies in how much to use to equate to one clove of fresh garlic; some brands recommend 1/8 teaspoon while others go up to 1/2 teaspoon.
For the most part, I found four brands to be the most similar: McCormick, McCormick Organic, Spice Hunter Organic and Frontier Co-op Organic. All four had a similar granular texture and tasted predominantly of raw garlic, so use them in place of raw garlic, being sure to bloom them in whatever cooking fat you're using to wake them up. Chef Merito was equal in texture but had a slightly more heady aroma, most likely from the added garlic oil in which the garlic was fried before being dehydrated.
When it comes to true powders, Spice Islands' white powder is mild and creamy, edging to more on the raw garlic side, while Burlap & Barrel's purple-gray powder is more earthy, with no raw garlic sting. Of all the powders I tasted, this one was the most outright aromatic, smelling assertively of lemongrass and toasted nuts. Use these powders to integrate smoothly into sauces, or sprinkle over fries or roasted vegetables as soon as they come out of the oven.
Morton & Bassett and Lawry's sell garlic powders mixed with dried parsley, a common combination for base, all-purpose seasoning. While both had the same scent of raw garlic mixed with the greenness of the parsley, Lawry's powder is slightly rounder and sweeter, most likely from being fried in oil similar to Chef Merito. Sprinkle them over freshly boiled and dressed potatoes for salad or mixed with butter as a spread over a roast chicken.
On the opposite end of the spectrum is McCormick's black garlic powder. Whereas other garlic powders contain garlic and sometimes oil, this seasoning utilizes a "greatest hits" collection of other umami flavors - cocoa powder, tamari soy sauce, yeast extract, tomato - to boost black garlic, a fermented garlic product that was trendy in restaurant kitchens several years ago but never achieved mainstream use in home kitchens. Tasting like a blend of balsamic vinegar, Marmite and grill char, it's a unique blend that would work well on tofu, chicken breasts and cauliflower or any other relatively bland food that could benefit from its grab bag of flavors.