It's a bit of a leading question, I know, but this question came up in a PHP Users group discussion and I was interested to see if there were any studies done comparing the two (regardless of who "wins").
I can see there are many tangibles to compare in licensing, IDEs, hosting, etc., as well as the intangibles of amount of time spent on tasks and so on.
It is also quite possible that this question has no merit and can't be answered...?