OK can I muddy the waters here just a little more?
I work for a car company now, and in years past worked in the off-road truck racing / parts business.
4WD is generally considered a system with a transfer case [center differential if you will] that mechanicaly locks the front and rear differentials. This type of system does not allow for any slip front to rear. This can casue issues with trying to trun a tight corner particulary in lo-range. Although some of these systems are electronic with a switch, many (most) have a transfer case lever in the driver’s compartment.
AWD is (again) generally considered to be a system that automatically transfers power front to rear, and allows for slip front to rear. Due to the slip front to rear, the turning circle is not affected by the operation of this system. This type of system may be mechanical OR electronic (my company makes both) but either way the system is automatic, no levers or switches.
Now car makers are free to call what ever system they market anything they want, I am just refering to generally what these systems are named.
You Liberty has TWO different drive systems? Don’t you mean that Jeep offers two different systems on the Liberty? if that is the answer then Command-Trac is a 4WD type system, and Selec-Trac is more of an AWD system. (regardless of what the Jeep marketing guys may call it.)
So what is best?
I agree with mmmiiikkkeee that the single most important factor is the driver. However given multiple drivers with comprable skill levels, my vote goes with electronic AWD prefferably with dynamic traction control. The current dynamic traction system we have updates what is going on and makes decisions once every 7ms. This is way faster than I can ever hope to control the car. If the car is getting out of control the system can apply individual brakes, regulate the throttle and if the laws of physics allow, make the car go where the steering wheel has it pointed.
About 4 years ago Car and Driver did a winter test between different types of cars in deep snow. AWD was the best followed by 4WD, FWD, and RWD last. the funny part was that when they turned on the electronic traction systems on the FWD, and RWD they got lots better, almost as good as the 4WD systems! need I mention that the issue of electronic control in cars has come a long way in the last 4 years or so.
A small personal note here. I live in So Cal and about 12 years ago when my kids were small, they wanted to go to the snow. So we packed up everybody in the car, an old Volvo with skinny tires, and off we went.
As we were headed up into mountains we started to encounter sleet and snow on the road surface. I was having no problems with traction, and had not yet considered stopping to mount tire chains. All of a sudden a 4WD mini-truck starts sliding across the road in front of me and hits the guard rail. WTF? We keep motoring, then it happens again a few miles later. Finally the raod got bad enough we did have to mount chains. By the end of the day we saw FIVE different 4WD trucks hit guard rails or go into ditches going no faster then we were. I started to think about this to come up with a reason, and the only thing I could come up with was the fact that all of these trucks have great big mudder tires. I suspect that the weight per square inch of tire area was so low that they would float across the snow and lose control. 4WD did not seem to be an advantage that day. 