Receptional_Andy - 10:05 pm on Jul 7, 2010 (gmt 0)
For me, the tool itself is of slight importance - I can happily process data in any number of ways. The important thing is how good the data source is for the purpose you intend to use it for.
I'd say for the overwhelming majority of usage scenarios, the Google tool is likely to offer the best combination of dataset/cost. If you want absolutely reliable data you need to either advertise or have a site that ranks.
The overwhelming majority of other tools do not have access to a reliable dataset. They are scaling data from a small number of users, or processing someone else's data in interesting ways. There's nothing wrong with that, but as I said, I prefer to process good data myself, than potentially rely on data that has been processed in ways that could be undesirable.