The value of Free

There is a lot of discussion in the games industry about free to play games, alternative business models etc etc. I have been giving some thought to the issue of price and how it impacts on perceived value and I just wanted to ask a question of those of you who have played a free game at some time (either online, iPhone or any other format - but excluding free demos/Lite versions)

Is your favourite game (or even your top 5) out of all the games you have played paid or free?

Basically I am just wondering how we value free versus paid for. Lots of people claim that "people don't want to pay" (especially kids) and yet my favourite games are the ones I have paid for. Just wondering what everyone else thinks.