As others have already mentioned, whole food is always the best option. But alot of people do throw in some protein bars occassionally, myself included.
If you must eat them, look for low sugar options and bars with as few ingredients as possible. I buy Kirkland brand protein bars from Costco. They aren't the best tasting if you're used to overly sweet processed food but it's like candy to me since I don't eat sweets.
The ingredient profile isn't terrible compared to lot of the crap out there. You have to get then directly from Costco though...they are marked way up on Amazon and other sites.