A good texting app for the iPod touch?

I had been reading/hearing on the internet about application that allows you to text from iPod touch but so far I seen only like two on the app store some were free and some are paid, but before I spend money on applications I would like to know which application is good to send text messages? I would appreciate any help that I could get, Thanks

Textfree unlimited or textnow ulimited, text+plus????