At the risk of upsetting just about everyone I think the most significant aircraft the RAF has ever operated is the Tornado in all it's guises.
I genuinely think it was a big and significant mistake.
F-4 and Buccaneer replaced by F-15A and E - we'd have been the canine's proverbials.
(Just prior to donning tin hat, gum shield and safety goggles I would like to state that I am quite aware that one has been 'the' war horse for many a year and the other proved that whilst turd polishing isn't possible you can at least get rid of most of the smell. But think what could have been....)