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Fact #1. The electric vacuum as we know it has been around for the better part of the 20th century. Its exact origins are muddied by patent disputes and snake oil sales histories. Crucially, however, the mechanisms for suction have been more or less standardized by now. That makes it a little easier to measure performance.
Fact #2. Suction power measurements are often referred to as air watts. They represent the actual suction power, not just the electricity consumed. There's an organization dedicated to developing these standards called ASTM International. They have a mathematical formula you can use to understand air watts. When buying a vacuum, that's what you should look for. Ideally, they will be in the high double digits.
Fact #3. Consider how much time you spend vacuuming. If the answer is less than thirty minutes, most models should suffice. Any longer than that, and there's a good chance you're being too thorough. Or you own a large enough home that you can splurge on a more expensive option. Or you're vacuuming a large workplace, in which case the owners should spend a little more. If you're on the cusp, make sure that you find an option that has impressive battery life.
Fact #4. You shouldn't worry too much about power. Battery powered vacuums are going to be slightly less powerful than corded options. But it shouldn't really be an appreciable difference. The standardized measurement of air watts helps. But so has the advancement in battery technology over the last few decades.
Fact #5. Brand names are important. They shouldn't be the end all, of course. But companies with more experience are generally better at making technological products. Especially if they have specialized. That doesn't mean you should just buy the first thing you see from a name you know, of course. But it should factor into your decision.