Now that I'm learning Arduino I've developed 3 Arduino robot kits. The first was fairly big and can take the Arduino Mega, Duemilanove or Nano. The second two have had the Arduino built directly onto the PCB so that little or no jumper wires are needed.
Which is better? The additional cost of the Arduino built in is less than buying an Arduino board and with all the basic wiring done it is much easier for those new to electronics.