[Locke.]

Only Fools and Horses is great and probably the best British comedy of all time but lets not pretend it's even half as good or half as popular as a worldwide phenomenon that gets over 25 million viewers per episode on a pay per view channel that is also contesting with illegal downloading and about 500 other channels. 2 million people watched the UK premiere of GOT at 2am a couple of weeks ago on SkyAtlantic, nobody would ever stay up that late to watch a sitcom for half an hour.

Game of Thrones has museums made after it, the Queen has been on set, its stars have gone on to huge movie careers despite the show still being on air, its boosted tourism in the multiple different countries it is filmed in, boosted book sales for the series it is based on, and is by far the most popular TV show of all time worldwide (much bigger than the other ones you mentioned that your friends have also recommended).