Torque Pro is definitely the best app, but it only runs on Android. For iPhone the app I use is: Car Scanner. OBD Fusion is also a good one for IOS devises.
Just look at the app developers info to determine the best OBD reader and compatibility for the app you want to use. I use the Veepeak Bluetooth scanner and it works well.
https://www.amazon.com/Veepeak-OBDCh...xGL&ref=plSrch
Whatever variety you like, definitely make sure you get a Bluetooth reader, not WiFi.