Which Spektrum Module?

[MRD]

Hi, I used to have a Hitec Aggressor with the origional spektrum module but this was stolen so I'm replacing it with a 3PK and was wondering which is the best spektrum module to get, there's the origional, the Pro and the 3pk HRS version.

From what I can gather the HRS version will only work with digital servos and the supplied receiver in HRS mode but can it be run in PCM mode to work with the older stuff?

The Pro seems to just be a better version of the origional but is there any compatability issues with the normal/older receivers?

Which is the best version that will work with all my other spektrum receivers and a mix of digital and analog servos?

Any help would be much appreciated .