I have been told the series landrover outlasted the willies jeep becaus the jeep had a c section chassis that was able to absorbe shocks where as the landrovers box section chassis could not and therfore made the driver take more care so as to make it to the end of the day themselfs. Its an interesting thought. likley based mostley on brand loyaltey as apposed any serious reserch.
IMHO the Willys Jeep was a much better vehicle than the Series I Land Rover. The Jeep was lighter, accelerated much faster, handled well, and was reasonably comfortable. In short it was fun to drive. You could do wonderful controlled slides and drifts on an unsealed surface. The Land Rover Series I SWB was a slug by comparison, very uncomfortable, but I suppose the best you could say about it was that it got the job done, perhaps in tricky going it may have been better than the Jeep but since I never got stuck anywhere in either it would be difficult for me to judge.