The Arduino Uno is the best board to get started with electronics and coding. If this is your first experience tinkering with the platform, the Uno is the most robust board you can start playing with. The Uno is the most used and documented board of the whole Arduino family.
Rev 3 of the Arduino Uno has the following upgrades:
1) 1.0 pinout: added SDA and SCL pins that are 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 with both the board that uses the AVR, which operates with 5V and with the Arduino Due that operates 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 Uno Rev 3 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 Uno. 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: 14 (of which 6 provide PWM output)
PWM Digital I/O Pins: 6
Analog Input Pins: 6
DC Current per I/O Pin: 20 mA
DC Current for 3.3V Pin: 50 mA
Flash Memory: 32 KB (ATmega328P) of which 0.5 KB used by bootloader
SRAM: 2 KB (ATmega328P)
EEPROM: 1 KB (ATmega328P)
Clock Speed: 16 MHz
Length: 68.6 mm
Width: 53.4 mm
Weight: 25 g
Getting Started: https://www.arduino.cc/en/Guide/ArduinoUno