There are two types of scales needed for most modernist cooking. A gram scale, for weighing out small ingredients and a kilogram / pound scale, for measuring large amounts of an ingredient.
I recommend electronic versions of each scale, they tend to be much more accurate and allow you to easily tare (reset) the scale so you can just add ingredients into the same bowl.
The kilogram / pound scale typically increase in increments of 1 gram which works well. A maximum weight of at least 2,250 grams / 5 pounds is ideal, and I prefer one with at least 10 pounds so I can easily weigh larger amounts of food.For the gram scale, an increment of 0.1 grams is normally good enough. Some scales increase by 0.01 grams, which is just fine, but probably a bit of overkill for most applications. The max weight is less important on the gram scale since most are above 100 grams.
If you want to get more specific, here are some more narrow categories of scales.
These scales are what we recommend to our friends and family. While one might be a better fit for you personally, you can't go wrong with any of them. These are mainly with a focus on home cooks (see below for professional machines).
Have you used something that we don't cover here? Let us know what you use and why you love it!