GE Jet Engines
Well - the CF6 used on the A300, A310, 747, 767, DC10 and later the A330 wasn't all that great in the beginning.
Due to its size (length) - the main shafts warped and damaged bearings. Early models couldn't be started in a tailwind or they'd over-heat.
These days the CF6 (747, 767 and A330 primarily) is more powerful and more reliable.
Its successor, the GE90 has upset people here and there - Like British Airways. Who were so disgusted with reliability they switched to Rolls Royce for some of their 777's. (And now there is the failure from their plane in Vegas...).
Overall though, the GE engines are typically some of the most powerful. The GE90 *IS* the largest engine in the world. I think it set the world record at over 115,000lbs of thrust.
The GE90 also happens to make a 777 vibrate like a tin can at start - which is pure 'symphony' for the enthusiast, like myself. Or freakishly scary!