perfect storm, page-20

WangChung

I've flown airplanes but never the heavy iron with the power-plants you're asking about. I took a Basic Gas Turbine course 20 years ago and this topic strangely enough came up with the teacher who was an ex 747 Capt with Qantas. This info is a little old and technology in terms of components and compositions will have been refined somewhat.

I believe the GEs give more bang for their buck in terms of efficiency but when talking about engines you need to consider other factors such as fuel flows at lower altitudes (jets are designed to run at higher altitudes thus climbing to 20 000ft + really costs fuel), thrust - weight limit which is the ratio at which a jet can pull at a certain weight before critical overloading on components needs consideration.
I believe RR has good post sales service packages, but the new Pratt and Whitney range claims to be superior to both and they've been around for a while as well. The old Dakota DC-3 (C-47 military) had 2 P&W Wasps as did the PBY Catalina.

A decent Google search will give you lots more...