The Arduino Nano is a small, complete, and breadboard-friendly board based on the ATmega328.
The MEGA 2560 is designed for more complex projects. With 54 digital I/O pins, 16 analog input.
Raspberry Pi 3 - Model B+ - 1.4GHz Cortex-A53 with 1GB RAM
RASPBERRY-PI3-CASE - Official Raspberry Pi 3 Case - Red and White