Well that is your first research problem. There are several 3rd party vendors that sell great Arduion compatable boards. They come in all sorts of packaging, some standalone like the 'standard' and others designed to pull into solderless breadboards. Some can be had for around $10 cheaper then the 'standard' so if price is a factor there are choices.
It really doesn't matter too much which you choose to start with, as if you have as much fun with it as many of us you will end up owning several versions. I'm waiting to see what the vendors have to counter the Arduino Mega myself and will then proceed with getting one or the other.
Lefty