If this is your first experience tinkering with the platform, the UNO is the most robust board you can start playing with. R3 board is a microcontroller board based on the ATmega328P (datasheet). The UNO is the best board to get started with electronics and coding. R3 board is a mainboard with almost the same functions as the Arduino Uno. Everyone makes clones, and can often make them cheaper (especially if they are in China and/or do not support our friends at Arduino). It has 14 digital input/output pins (of which 6 can be used as PWM.

The UNO is the ideal, entry-level board for those who are new to developing on the Arduino platform. The Arduino Uno Rev3 is a microcontroller board based on the ATmega328 (datasheet). The UNO also demonstrates the basics on sensors and actuators. It is a perfect introduction to electronics and coding. This product officially supports the Arduino environment and IDE. The Arduino UNO is a development board which features the ATmega328P microcontroller (MCU). It has 14 digital input/output pins (of which 6 can be used as PWM outputs). Except this isn't an Uno R3 compatible board. The Arduino Uno is an 8-bit microcontroller board based on the ATmega328 chip (see the datasheet). Instead, it features the Atmega16U2 programmed as a USB-to-serial converter. Arduino Uno is a microcontroller board based on the ATmega328P (datasheet). The Uno R3 differs from all preceding boards in that it does not use the FTDI USB-to-serial driver chip. Note that the two ICSP headers are separately used to program the firmware to ATMEGA16U2-MU and ATMEGA328P-PU, but generally the two chips have been programmed well. It has 14 digital input/output pins (6 can be used as PWM outputs), 6 analog inputs. It contains everything needed to support the microcontroller simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started. Arduino Uno is a microcontroller board based on the ATmega328P (datasheet). It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz quartz crystal, a USB connection, a power jack, 2 ICSP headers and a reset button. Keyestudio Uno R3 is a microcontroller board based on the ATmega328 (datasheet), fully compatible with ARDUINO UNO REV3.

Arduino uno r3 board datasheet