I2C vs. SPI: Which language should your project speak?

Choosing between I2C and SPI often comes down to balancing speed against pin count. 

I2C is the go-to if you are trying to save board space because it only requires two wires, SDA and SCL, no matter how many sensors you add. It uses a clever 7-bit addressing system and provides peace of mind with ACK and NACK bits that confirm your data actually arrived. Anyway, it is generally slower than SPI. 

If your project involves high-throughput components like displays or flash memory, SPI is the better choice. It typically requires four wires and uses a dedicated chip select line for each device. The big win with SPI is its full-duplex capability, allowing it to send and receive data simultaneously at much higher speeds. 

Basically, you should pick I2C for simplicity and a smaller footprint, or SPI when your application requires actually raw performance.