bizzarely, I'm going to buck the trend here, and say 3
Given that your daughter is so young, it will be a good few years before she is going to be getting in and out by herself.
With that in mind - to put her in her seat in a 5 door, you are lifting her in from the side, and then having to reach over and around her for the straps.
With the 3 door, you put her in almost from the front, making it (I believe) much easier
Plus you don't have to worry about her playing with the window controls in the back
Really though, your best bet is to turn up at dealer with childseat and child, and give it a go