The Arduino Mega 2560 is designed for more complex projects. With 54 digital I/O pins, 16 analog inputs and a larger space for your sketch it is the recommended board for 3D printers and robotics projects. This gives your projects plenty of room and opportunities.
Rev 3 of the Arduino Mega 2560 has the following upgrades:
1) 1.0 pinout: SDA and SCL pins - near to the AREF pin - and two other new pins placed near to the RESET pin, the IOREF that allow the shields to adapt to the voltage provided from the board. In future, shields will be compatible both with the board that use the AVR, which operate with 5V and with the board that uses ATSAM3X8E, that operate with 3.3V. The second one is a not connected pin, that is reserved for future purposes.
2) Stronger RESET circuit.
3) ATmega 16U2 replace the 8U2.
The Arduino Mega 2560 does not use the FTDI USB-to-serial driver chip used in past designs. Instead, it features the ATmega16U2 programmed as a USB-to-serial converter.
Note that this is the official version of the Arduino Mega 2560. While the price is higher than the clone boards, you can be sure of the reliability and compatibility of this official board with your computer & project.
Operating Voltage: 5V
Input Voltage (recommended): 7V to 12V
Input Voltage (limit): 6V to 20V
Digital I/O Pins: 54 (of which 15 provide PWM output)
Analog Input Pins: 16
DC Current per I/O Pin: 20 mA
DC Current for 3.3V Pin: 50 mA
Flash Memory: 256 KB of which 8 KB used by bootloader
SRAM: 8 KB
EEPROM: 4 KB
Clock Speed: 16 MHz
Length: 101.52 mm
Width: 53.3 mm
Weight: 37 g
Getting Started: https://www.arduino.cc/en/Guide/ArduinoMega2560