Well Merseyside is a big area and extends well beyond the City of Liverpool itself, so i don't know
But in Liverpool there's definitely an Everton majority, on Liverpool home match days the town centre gets jam packed full of Liverpool fans mainly from Scandinavia, Ireland and the far east
Everton have in Liverpool.
Liverpool is a worldwide club whereas everton is not.. So liverpool have more fans
I would suspect Liverpool as they have won more. It will be like going round Madrid and asking who's more popular RM or Athletico, the answer would be obvious.
In Mersey side are the majority of people Liverpool or Everton fans?