That question is not that easy to answer.
The British Empire, influential as it may have been, is not necessarily the most influential. The English language for example is spoken worlwide
not because of the British Empire. Most scholars are of that opinion. The English language was never been spoken in the areas the British occupied. It was only spoken in that areas by the British and a small part of the assimilated elite. The school curricula including English mostly failed in that time.
The main reason for the worldwide use of the English language today is a different one: the western world has been under the influence (politically und culturally) of the United States for the last 60 years, for example the development of modern communication via computers and internet was driven (while not always spearheaded) by the United States, thus the language evolving and revolving around it was English, same goes for international alliances like the NATO. Furthermore is the English language far easier than all the other languages that played a role equally as big as the English language (German, French, Spanish etc.), that's probably the only reason it's the official language of the European Union. For example German and it's "Verstehensgemeinschaft" (perhaps "comprehension family"), which means the languages you can understand or easily learn, when you can speak German, like Low German, Dutch, Yiddish, Cape Dutch (Afrikaans), Luxembourgian etc., are spoken by far more people in the EU than English. Almost the same goes for French. (Sorry, my British friends, but that's the truth.)
Not only the Romans had an empire with a modern bureaucracy and administration, but the ancient Chinese as well. The Chinese writing system influenced or even established writing systems in Korea, Japan, Vietnam, Thailand etc. and Chinese buddhism migrated into the whole world, making it one of the biggest religions. In the last 3,000 years, the Chinese empire was most of the time the biggest existing empire in population and landmass.
Germany and Italy influenced the world as it is today in a way, that most people fail to recognize on a regular basis. A huge part of the most influential discoveries and inventions go back to Germans/Italians or German/Italian immigrants in other countries (from the
axe to the
wire to the
telephone (yes, we had that 16 years before Bell, believe it or not

). The German (Prussian) school system was "exported" into as many countries as no other school system on this world. So was the German and American military system.
German, Italian, Dutch and French art was way more influential than British art. German writers like Friedrich von Schiller, Johann Wolfgang von Goethe or Gotthold Ephraim Lessing were at least as influential as Shakespeare. Goethe was in many respects at least as influential as Shakespeare, he even helped Shakespeare to fame through his famous Shakespeare critique, where he praised Shakespeare's rich use of words and stylistic devices (even though Goethe used 78,000 words wheras Shakespeare only uses around 35,000). And how can anyone forget artists and musicians like Leonardo da Vinci, Michelangelo Buonarroti, Vincent Willem van Gogh, Jan Vermeer, Eugène Delacroix, Albrecht Dürer, Pierre-Auguste Renoir, Peter Paul Rubens, Wolfgang Amadeus Mozart, Johann Sebastian Bach, Ludwig van Beethoven, Joseph Haydn, Richard Wagner, Johann Strauss etc.. none of them British.
Or our modern economic system: it may have been influenced by the industrial revolution which started in Great Britain, but that industrial revolution would have never taken place without it's predecessors (French mercantilism and physiocratism or German cameralism) or with modern capitalism, which was way more advanced in Belgium, Germany, the Netherlands or northern Italy than in Great Britain by the time the East India Trading Company set sails for the first time.
In short: just plainly saying "Great Britain" is not merely enough.
The US also spent 180 years of largely staying out of the affairs outside of the Americas, although that changed after the Suez Incident of 1956.
Since then I'd strongly argue we've been a victim of our own set of follies, much in-line with the Romans.
Not true. The US already interfered in other countries business with what they called the "Splendid Little War" and through Theodore Rossevelts "big stick policy" (speak softly but carry a big stick). That was more than a hundred years ago.
And while the politics and policies of the Roman empire and the American empire are quite similar at times (metus gallicus metus punicus for example), they differ very much in certain other areas. Even though the Romans were spread too thin at the end (almost like the US is now) the Roman empire collapsed mostly for different reasons as well (for example the "new religion" called christianity or the partition).