Sometimes the most obvious solution is the best solution.
I believe your absolute best option is to use the AdWords conversion tracking feature. The main reason is that having that data within your AdWords account allows you to use that data to automate scripts. And using the AdWords tracking script does not prevent you from using any other tracking software. You can still use Google Analytics, which is designed from the ground up to integrate with AdWords, giving you even more detail in both your AdWords account as well as Google Analytics.
Google Analytics works well for tracking data from all other marketing campaigns, it’s not just for Adwords. You can use Custom Campaigns to track results for any kind of campaign, on nearly any kind of platform.
Now there is one thing that Google Analytics is not good at and that is tracking individual visitor paths. Due to privacy concerns, Google analytics anonymizes data by only reporting aggregate visitor data. To gain the further insight you will want to use an additional analytics package. A good option for more in-depth visitor data is an open-source program called Piwik.
