The difference of 4x4 and AWD to me is the turning radius. I had a 98 Chevy Astro van AWD and I could turn that rig without any problems. I traded the van in for 98 Ford F150 4x4 because of towing issues and I have noticed that the F150 when put in 4x4 does not do slow tight turns very good. I can feel the U-joints binding. I suppose it is because the AWD is made more for constant motion and 4x4 is made more for heavy duty work.
I prefer the AWD, but like Monkey44 said before, "If you only ONCE need a real 4x4 drive line, you'll learn the difference in a hurry".
There are actually 4WD which switch in and out of 4WD as needed and their is a separate selector position provided. Handy when going through patches of snow on an otherwise dry road. AWD works in this fashion providing power to the wheels as needed.
The biggest differences with 4WD is that it can be fully off so the front wheels can turn without turning the front differential or affecting the transmission, and the previously mentioned option on some of a low range.
I love the low range as it enable the vehicle to go at a quarter of the speed as in high range with the same engine RPM's for power. Often in rocky terrain or when going across a stream I will be in low range and moving at 1-3 MPH with all the power I need from the engine. It is easier on the drive train and the passengers and if I hit something at 3 MPH the likely damage is much less than if I hit the same rock at 15 MPH. The shocks also work better with slow motion movement of the vehicle on bad terrain and there is less chance of the vehicle bottoming out. With a manual transmission there is no need to slip the clutch with the low range setting to keep the speed of the vehicle down.
AWD is going to have less impact on the gas mileage of the vehicle and add a lot less weight which is why it is used on sedans and small SUV's.
Subaru is the only AWD vehicle I know of that actually does not have a true "transfer case"
Nearly all other AWD or 4WD vehicles have a transfer case between the front and rear drive shafts (there may be some others that don't have one, that I don't know about).
IIRC (remember, I'm working with a senior memory ), Subaru's that were sold in Australia were available with a HI-LO transfer case. But, of course, they wouldn't be available in the good ol' USA....
We had a '95 Jeep Cherokee that you could put the transfer case into 4-wheel drive up to about 60mph with no problem, "Slick as snot..."
2000 32' HR Vacationer with Banks
1998 Subaru Outback Ltd. 5 spd
Brake Buddy & Blue Ox Aventa II tow bar
FMCA #266040 HRRVC #84109