I would suggest go with Arduino first, I installed AVR Studio last night having used Arduino for three months. I haven't got any code onto a chip yet with AVR Studio but can already see there are many more configurations I will need to work through before I do. With Arduino it was pretty much plug and play.
The Arduino libraries also give a nice introduction to the underlying hardware, for example if you read through the source code of the Servo library you will learn a lot about the interrupts and timers. This is all knowledge that you can carry over to AVRStudio as and when you decide to.