Which version of pixhawk should I buy? 1 or 2?

Hello ! I need a pixhawk for my project. I wanted to know which version should I buy pixhawk 1 or pixhawk 2? I wanted to play with the autopilot for my project (will be trying to control rotor speeds rather than sending roll,pitch and yaw commands)

I like the pixracer 'cause it’s small, has new sensors, and has a port for a Wifi link. But perhaps it doesn’t have enough I/O for you?

Yes ! I need more I/O. I was wondering whether I should opt for pixhawk 1.8 or 2.1?