As far as revenue earned, the 744 wins hands down. The stretched upper deck gives more seats, usually the high margin business or first class seats. Its a two person cockpit, so they are saving the cost of an entire senior crewmember. The engines on the 744 are newer and more efficient designs than those on the 742, so they drink much less fuel over the same amount of time.
But, if we get into the questions of financing the birds, then things get a lil complicated. Most 744s are still being paid off, but almost every 742 is wholly owned by the company (unless it is leasing them). Since there are no payments to make on the bird, the 742 might come out ahead there, but I think the savings from the newer tech on the 744 would probably mitigate this.
Again, these are just my thoughts. I don't have exact figures.
Excuse me, but what does God need with a starship?