There are many makes and models to choose from when shopping for a scale. The most common types on store shelves are spring scales and digital scales. My money is on the digital variety. Spring scales are easy to use, but some of the spring type may have difficulty registering small amounts of ounces or see more wear and tear on parts versus the digital scale. Spring scales may be cheaper, but consider the features available on digital scales. Today's digital scales can have handy functions like metric-customary conversions, fraction-decimal conversions, or even some models may have the specific feature of measuring liquids based on a liquid's unique density. While each cook will need to decide what is important for them, I ultimately look to three major factors - tare functionality, sizeable maximum weight, and accuracy,
The tare function is a great feature that extremely useful. Taring sets the scale back to 0. This aspect will allow you to ignore the heft of mixing bowls or weigh individual ingredients as you add them in.
Another consideration when choosing a scale would be the scale's maximum weighing capacity. With a large enough max load, you don't have to weigh ingredients before adding them to a bowl; you could put the work bowl on the scale and weigh as you go. Think about the size of your work bowls - the scale will bear them along with the recipe elements.
Accuracy. There's no point in owning a scale if it doesn't work properly. This is why I like digital scales - accurate and I don't have to adjust anything. I'm a klutz, so I avoided a manual scale I could blunder with. Also check to make sure you can read the output. Tools are to help, not make things more difficult.