Which app will give you the best traffic for your area will vary. So if you want the best, try a little.
I'll start with just looking at the built-in Maps app. For most people it will work well. You can also download the Google Maps app and it also has traffic. Also other third-party maps and directions apps like Waze and MapQuest.
You may want to look at the apps offered by the local city's news network. Sometimes they also have traffic, which can give you more detailed information about specific events if that is what you are looking for.