Why does same wifi gives different speed for different devices?

Some devices have different types of WiFi recievers taking in the signals and it is also the type of connection the receiver takes and the router puts out varies speeds also. The best type of connection I'm reffering to is the 802.11n connection type which is the fastest connection type off of wifi because it keeps the internet signal going through focused on the wifi signal output! 

Exactly what he said he smart