You should get lots of opinions on this one.
Personally I think the worst thing you can do is to drive a brand new car down the highway droning along at 70 MPH for hours at the same RPM.
When I used to race karts, my engine builder was the lead engineer who designed the V10 in the viper. He had a dyno at his house and built kart engines on the side. Actually he would have argued that he designed viper engines on the side as he loved building the kart engines
Anyway, his theory was this...
Heat cycles are good. So lots of short trips during the break-in are preferable.
High revs are bad (especially with low load). But don't take that to mean baby it. You want to progressive add manifold pressure (high load at low and moderate RPM). So in a manual trans vehicle, you might start doing half throttle accelerations from 2,500 - 3,500 rpm in 5th or 6th gear. Then after maybe 50 miles, start doing full throttle accellerations from 2,500 - 3,500 RPM in 5th or 6th gear. Give the engine 5 minutes of normal driving between "pulls" to give it time to cool.
Those high load, low RPM pulls create high cylinder pressures which help the rings seat.
