Arduino - Mega or Duemlianove Answered

I have been thinking about getting an arduino from Adafruit Industries. They carry two - The arduino duemlianove with the Atmega328 and the more powerful Mega with atmega1280 chip. I am having difficulty choosing between the two microcontrollers.

My main focus will be on larger projects like the Garduino(www.instructables.com/id/Garduino_Gardening_Arduino/) but again also on smaller robotics projects like advanced balancing robots(multiple accelerometers and sonar sensors)or even arduino smart drones(aircraft).Some of the factors in my descision will depend on:

• Price
• Weight
• Dimensions
• Power requirements
• Flash ROM
• Output pins
• Protoshield/other shield capabilities
• PWM control
• XBee wireless support
• Integration with logic systems
• Support for multiple(3) LCD screens/Dot Matrix displays
• Multiple Servo support
• Sound/Media support

Please help me choosing this microcontroller.I will only buy once in maybe 4-5 years so I want it to be good buy.

Also tell me which shields should I buy for my requirements: either the sound shield or the servo shield.I think I will buy the servo shield because it will give me greater control over my robotcs projects

Kabir