We utilize Dataflurries tracking software to ensure all of our clients are being tracked correctly! They have been able to help us track performance across multiple websites (which I haven't found anywhere else).
There isn’t much that we dislike about this service but it could be better for mobile reporting - which would make my job easier in terms of time spent collecting data. If you're looking into tracking your traffic using their API's then definitely check them out first!! Great support team with tons of resources available if needed as well.