The main difference is SERIN2 is all software(bit banging) while USART is done in the on chip hardware.

SERIN2 has the advantage of being able to be used on just about any pin and can be setup for Inverted or True mode.

USART has the advantage of running in the background and can be used as an interrupt trigger.

Sometimes considered a disadvantage the USART is True mode only so depending on the application an inverter chip might be needed (MAX232 type).

Data with both types can be a standard 8N1.

To be honest I have not really looked at your code but I will guess some sort os simple checksum would solve the noise problem. I will take a look at it later.

Reliable RF can be used with bit banged serial, Bruce has a nice example in the Code Example section.