Hi everybody, I have

MacBook Pro i7,
4 cores 2,6 Hz,
SSD 512 Gb,
8 Gb RAM,
Retina Display,
OS X Lion 10.8.2.
64 bit
Firewire 800
USB 3.0

I want to buy one of this RME:

Fireface UCX
Fireface UC
Fireface 400

Could you please help me to make the choice.
I need one the most suitable for my Mac, considering specification of my computer and drivers availability for my OS - to provide the lowest latency.