Us, without a shadow of a doubt. We're not only the biggest club in the West Midlands, we're the biggest club in the entire area between London and Manchester. We have one of the biggest and best grounds in the country, the best training facilities, an excellent academy set up, and have spent the (joint) longest amount of time in the top flight out of all the clubs in England.
And yet, in the last one hundred years, we have won the league once and the FA cup twice. Yes, Rotterdam was a huge achievement. Yes, it's nice to have won the league cup a few times. But as far as domestic competition goes, in the last century we have underachieved dismally.
Teams with more league championships in the same time period:
Manchester United - 18
Liverpool - 17
Arsenal - 13
Everton - 8
Chelsea - 4
Leeds United - 3
Wolverhampton Wanderers - 3
Manchester City - 3
Huddersfield Town - 3
Tottenham Hotspur - 2
Derby County - 2
Portsmouth - 2
Sheffield Wednesday - 2
Blackburn Rovers - 2
Burnley - 2
Still...Up the Villa!