I would go for chicks for sure...you can not beat watching them grow up from itty bitty balls of fluff. And if you only want 4, you probably won't get that chance again for a while.
Positives to getting chicks:
Building a brooder is super super easy and very cheap. I use a large cardboard box, all you will need to buy would be a something to put the food and water in and a heat lamp. You can find other ideas, information, and designs in the other forums.
When you raise them yourself, not only do you get the chance to watch them grow and learn about them little by little, but you become familiar with their characters so they will be better "members of the family".
When you handle them from day one, they are SO much tamer.
I would pick different breeds, so you can tell them apart easily and enjoy different characteristics of them, or different egg colors. They make better eye-candy this way.
It is much cheaper to buy chicks than grown pullets.
Negatives to gettting chicks:
It can be expensive or difficult to only get 4 from any place. Expensive to order online, and most stores will make you buy at least 6.
There is always a chance that one of your sexed "pullets" might turn out to be a rooster.
You will have to spend more money on food and wood chips and other supplies before you will actually get any eggs from them.