OBD-II readers and ABS scanners perform different functions. Basic OBD-II readers read the codes your car displays in order to diagnose specific problems with your powertrain. These could include engine, transmission and oxygen sensor failure codes among many others. An ABS scanner performs a similar function but pertains to your brake system, and sometimes also diagnoses any problems with your airbags.
There are many combination OBD-II and ABS code readers on the market. These are usually more expensive than standalone readers but have the added benefit of complete home mechanic car diagnosis. Some producers of these combination scanners are Actron and Autel.
Which device is better depends on what your needs are. If your ABS light is on and you want to find out what the problem is before buying parts or turning your car over to a mechanic, buy an ABS scanner. If your check engine or other warning lights are on, you'll need an OBD-II reader to diagnose the problem. Buying a combo device, while more expensive, ensures you will cover your bases in case of future problems.
