Dedicated iPhone twitter app, or just the SMS app?

This is for anyone who uses twitter and has an iPhone. Do you use a dedicated twitter app, or do you simply use the iPhones SMS app, and receive tweets over text message?

Has anyone gone from using one, to using the other? What benefits do you see for your current system?

I use the default SMS app, but I can’t help but think there must be a better way. I would like to be notified each time I receive a tweet, but not from every one of the people I follow, just from the people I send to my phone now. Is this possible?

Also, what is the best iPhone twitter app in your opinion?