I suspect this is going to generate some debate.
 
  1. It's based on Neilsen TV markets (and estimation of TV market for Toronto and Montreal).
  2. I've considered the top 50 US TV markets plus Toronto and Montreal.
  3. I've made educated guesses at what fraction of markets outside their home to assign to teams; thanks to everyone who's given me suggestions on those.
  4. I've made educated guesses on how to divide up the two team markets with the presumption that some people can be (at least casual) fans of both teams.
  5. I'm willing to adjust the rankings for accuracy or reasonableness, but I've tried to solicit suggestions before putting any numbers here to avoid people trying to make it "come out right".
What I discovered:

When looking at market size as "number of TV households", I found basically three groupings: large market teams (with >130% of average market size), small market teams (with <=70% of average size), and a clump in the middle. I'm going to list them here, along with their market size (as a percentage of average), which markets they cover (with percentages), and how those markets rank among the top 52 US markets (plus TOR and MON).
 

LARGE MARKET TEAMS

  1. New York Yankees
  2. New York Mets
  3. Los Angeles Dodgers
  4. Boston Red Sox
  5. Anaheim Angels
  6. Philadelphia Phillies

MEDIUM MARKET TEAMS

  1. Baltimore Orioles
  2. Seattle Mariners
  3. Chicago Cubs
  4. Texas Rangers
  5. Atlanta Braves
  6. Toronto Blue Jays
  7. Florida Marlins
  8. Detroit Tigers
  9. Chicago White Sox
  10. Tampa Devil Rays
  11. Houston Astros
  12. Cleveland Indians
  13. San Francisco Giants
  14. Montreal Expos

SMALL MARKET TEAMS

  1. Minnesota Twins
  2. Cincinatti Reds
  3. Arizona Diamondbacks
  4. Oakland As
  5. Colorado Rockies
  6. St. Louis Cardinals
  7. Pittsburgh Pirates
  8. San Diego Padres
  9. Milwaukee Brewers
  10. Kansas City Royals


That's it. Two real outliers at either end of the scale.
 

ODDITIES

  1. Biggest market without a team: Washington (8)
  2. Biggest markets really without a team: Sacramento (22), Orlando (24)
  3. Markets with no claims: Nashville (32), Salt Lake City (38), Birmingham (41), Norfolk/Portsmouth/Newport News (42), New
Orleans (43), Greensboro/Winston-Salem/High Point (49)