Quest is the bar most people should simply default to, and it earns that status. It delivers 21 grams of genuinely complete protein from whey and milk isolate with no collagen padding, just 1 gram of sugar and 4 grams of net carbs, in flavors you can find at virtually any store. It quietly reformulated off the much-criticized IMO fiber years ago onto soluble corn fiber, so the macro story holds up better than most of its low-sugar rivals.
It does lean on sucralose and erythritol, so it isn't an all-natural pick, and the texture is on the dense, chewy side. But for a complete-protein, low-sugar bar that's affordable and available everywhere, it's the easiest recommendation in the category.