And Rutan
preferred two...
There are many trade-offs to decide if one engine is better than two, the peacetime serviceability rates being only one. Then case was made that, if you did the maths for purchase price, running costs, MLU etc, over the life of an aircraft, that a single engined type was still cheaper even if additional aircraft were lost. However if you were the pilot floating down over the middle of the Bering Sea that might not be of great comfort.
There is also the factor of battle damage. The USN took heed of the number of F-18s which came home in GW1 with damaged tail-pipes and engines against the loses of AV-8Bs - and I am aware that was attributable to the nozzle locations of the Harrier making it susceptible to IR missiles.
I don't believe there is a knockout technical argument on either side. If you have to have VSTOL, then single engine is the only realistic option. If, like Canada, you don't, then it comes down to preference.
Having two engines does bring it's own problems. If you separate them then single engine handling issues, a la the Canberra, can cause losses. If you put them together then the failure of one can take out the other. The F-111 cured that by placing a large, heavy, titanium sheet between them. I saw one that landed at Newcastle with the entire fuselage ripped upon on one side. Impressive that it managed to keep flying.