If you can avoid rotating in place, do so. Here's two identical M4A3 Shermans. The tank on the left is ordered to rotate 180 degrees while the tank on the right is given the shortest and simplest possible U-turn orders (Quick).
33 seconds later the U-turn tank is facing south while the rotating tank is still turning. The rotating tank would take 44 seconds to complete his turn, as in POS's test above (even though I'm on open ground and POS was on dirt road). Performing a U-turn, even a lazy one, is still 25% faster than pivoting in place.
This time I try rotation versus a much longer, but smoother route (Quick):
Even though the U-turn tank travels much farther than all of the other tests, the smooth waypoints more than make up for it. He is back facing North in only 20 seconds -
less than half the time it takes to rotate. You can see how far along the rotating tank is, by comparison.
Conclusion: Avoid rotating in place if you have room to maneuver. The smoother you can make your waypoints, the faster you will go.