From what I remember, though, I believe King Lemming said that a lot of TE was designed to be as CPU-friendly as humanly possible. That said, I'm not sure about the exact performance stats of generators vs engines...specially since both require wiring to use/store the energy, anyway.
Well consider that in my setup I was using 300 thermal generators for continuous power (I was rapidly depleting an enormous area in a lava age with 4 advanced pumps). If I switched to magmatics for greater fuel efficiency, I'd need 800 of them to produce the same rate of power. CPU friendly or not, it's 500 more power producing blocks, plus the wiring and power converters (although conversion of bc to hv would reduce the number of eu packets dramatically). My own solution was to switch to boilers and power convert steam instead (because I need only 14 of those to produce about the same rate of power).