I switched to the RXS Carbon from Look Keo about a year ago. I like them a lot but both are great choices.
Getting out is about the same if you use the red cleats on the Look. The Look can also be used with 0 float (black cleats) or "in-between" (great cleats).
The RXS only have one type of cleats with both lateral and angle float. They seem loose at first but are actually very secure and comfortable.
If you have wide feet you will prefer the RXS with their 2 options for q-factor (distance between pedal and crank arms. I used to have washers between the pedal and arms with the Look.
To me the most important difference is getting in the pedals. With the Look I used to miss the re-entry if I was hurrying things and often ended up hitting the back of the pedal resulting in my foot slipping off. I have yet to miss a re-entry with the RXS, the pedal is always is the correct position