The board most people learn on, and the one most projects ship on. The ATmega328P is forgiving, the pinout is documented everywhere, and almost every shield and tutorial in existence targets it. Fully supported in the Lab simulator - prototype the sketch in the browser, then flash the same code to this board.
Specifications
| Microcontroller | ATmega328P |
| Clock speed | 16 MHz |
| Digital I/O | 14 (6 PWM) |
| Analog inputs | 6 |
| Flash / SRAM / EEPROM | 32 KB / 2 KB / 1 KB |
| Operating voltage | 5 V |
| Input voltage | 7-12 V |
| USB | Type-B |
Ships with the bootloader pre-flashed and headers already soldered.