I've got one for those who love Statistics:

We have a list of WHS that have been 'ticked' most by our community members. The top 10 at the moment is:
1 Paris, Banks of the Seine
2 Rome
3 Westminster
4 Tower of London
5 Amsterdam Canal Ring
6 Vienna
7 Vatican City
8 Venice and its Lagoon
9 Florence
10 Prague

Nomadmania has a similar list. Their top 10 is:
1 Historic Centre of Rome
2 Historic Centre of Prague
3 Vatican City
4 Historic Centre of Vienna
5 Paris, Banks of the Seine
6 Tower of London
7 Budapest
8 Historic Centre of Florence
9 Venice and its Lagoon
10 Historic Areas of Istanbul

The Amsterdam Canal Ring is somehow missing from the NM list, while Amsterdam as a city ranks 3rd among all cities! The relatively low ranking of Paris is also notable. And the Tower of London is at #6 but Westminster only comes at #14 (it would be hard to miss the Big Ben when you're in London...).

Any other observations? It may also lie in a different member base. Our is somehow centered around Germany and the Benelux. That of NM seems to be more to the East.

it is hard to believe that London visitors visit Tower of London more than Big Ben. The clock tower is more iconic, and it is free! I think the problem is the official name of WHS, most people don't have time to look in details what is include and exclude from those description. For example: What is the Seventeenth-century canal ring area of Amsterdam inside the Singelgracht? Where is Singelgracht? I only know Dam Square.

For the TWHS the comparison is as follows: our website (made a new stats page for this):
1 Central Park
2 Historical Lisbon, Global City
3 Brooklyn Bridge
4 Le Palais de Justice de Bruxelles
5 Dreams in Stone - the palaces of King Ludwig II of Bavaria: Neuschwanstein, Linderhof and Herrenchiemsee
6 Les passages de Bruxelles / Les Galeries Royales Saint-Hubert
7 Mdina (Citta Vecchia)
8 Knights Fortifications around the Harbours of Malta
9 Ellis Island
10 Amalienborg and its district

Nomadmania:
1 Central Park, New York
2 Brooklyn Bridge
3 Historical Lisbon, Global City
4 Tbilisi Historic District
5 Ancient Greek Theatres
6 Extension of the World Heritage Site "Historic Centre of Prague"
7 Mdina (Citta' Vecchia)
8 Jerusalem*
9 Þingvellir National Park
10 Gdansk - Town of Memory and Freedom

That extension of Prague is very suspicious. As it is so specific (villa Müller, abbey and park) and outside of the busiest centre, I am not really sure it was ticked with awareness...

It ranks 21st here, which makes more sense.

Yeah I would imagine it is the less WHS specific focus of Nomadmania that may lead to a few of the differences.

I've been to Prague 20+ times and haven't properly visited the extension, so I imagine someone may just see Historic Centre of Prague and just assume it is extending the core zone by a few more roads.

And yes Tower of London being ahead of Westminster seems odd, again perhaps it is the more specific name for the Westminster WHS that leads to the difference.