The PS3 and the Xbox 360 both have a text pad accessory to attach to the controller.
The PS3 text pad is on top of the controller, i think. While the Xbox controller's text pad is on the bottom.
Which is easier to type with, while playing games?
Personally I'd say neither would be the most comfortable to type with, the xbox's keypad kind of gets in the way of were you grip the controller and the sony device kind of gettings in the way of your shoulder buttons.
Personally when i'm using the PS3, I find the best thing thing to use is just a standard USB Keyboard. It allows for quick and easy typing, doesn't get in the way of the controller, and a USB keyboard is a lot cheaper than the add on device for the controller.