After posting, I thought again about the breadth of Brunel's achievements and I agree, he would get my vote as the greatest.
That's not to take anything away from Sir Stanley. As well as the Orpheus and other turbojets, there's his work on the Merlin and Griffon superchargers.
For those that either don't know or haven't read the book, he was a theoretical scientist and one of the leading experts in fluid dynamics, with no practical experience at all. What nobody knew, including Lord Hives who employed him at Rolls-Royce, was that this also made him an expert on supercharger design, and later, on gas turbines.
As well as the Orpheus, there's the Olympus, the Pegasus using the Orpheus core, and he led the team that redesigned the RB211 to become an extremely successful engine. I understand the huge 100,000lb range engines that RR are building now can still be traced back to the revised RB211 he and his team designed in the early 70's.