-Abs is less brittle, which is better for some parts.
-Abs has a higher melt point, which is good for parts that are used outdoors in on hot days.
-Abs is smoother and more naturally lubricated which makes it less likely to jam an extruder and puts less wear on your nozzles

That said, there are lots of alternatives these days that give ABS a run for it's money in these areas as well.