I use Nistune and like it. It didn't cost me much at the time ~ $350.00 (without a cable which I already owned). It has the ability to data log the sensors on your car. You can add a wideband O2 sensor (or 2) which it can also log. Using Nistune you can log your wideband AFR against RPM and Load (key stats to tune your car). Nistune also permitted me to attach a DLP IO 8 which I use to log my boost pressure via a more accurate pressure sensor. In addition to all the logging it also provides real time tuning. So you can log, adjust your maps and log again to see what your changes have done.
One item that I don't like is the forced S/W upgrading every 6 months. The good news is the upgrades are free and it is great that new features are being added all the time, but it does require you to relearn the software when you upgrade since typically there are changes to the menus etc. I just use the core features (which have always been there) so upgrading for me is more of a chore.