The top four teams in AAA in terms of attendance right now are Sacramento, Round Rock (Austin market), Memphis, and Louisville. All but Louisville play in the Pacific Coast League.
Louisville is the smallest media market of the four (not even in top 50), despite having rich baseball heritage. The Cubs, Reds, and Cardinals would likely lobby hard against a team in Louisville as well.
Memphis is only slightly larger than Louisville. Memphis would likely only make small dents in the fan bases of Atlanta, Saint Louis, and Texas.
Sacramento is a considerably larger market. The two teams most affected by a Sacramento club, Oakland and San Francisco, share the nation's fourth largest market. San Jose, just down the road from San Francisco, is a larger media market than Indianapolis, Las Vegas, Louisville, and Memphis.
Austin, while not as large as Sacramento, is still larger than Memphis and Louisville. It's close enough to San Antonio as well to draw fans from there. Houston is the fourth largest market in the U. S., so the Astros shouldn't hurt too much from having a team ~80 miles down the road.
Portland and Charlotte each average about half the attendance Louisville does.
As far as realignment goes:
AL West: SEA, SAC, OAK, LAD, TEX, AUS
AL Central: KC, MN, CHW, DET, CLE
AL East: TOR, BAL, NYY, BOS, TB
NL West: CO, SD, SF, LAA, AZ, HOU
NL Central: STL, MIL, CHC, PIT, CIN
NL East: PHI, WAS, NYM, ATL, FL
You can move Round Rock (Austin) and Sacramento to Montreal and Edmonton.
Dayton (Midwest League, A) and Springfield, MO (Texas League, AA) pick up AAA expansion teams. Montreal moves to the International League, joining Dayton, while Springfield joins the Pacific Coast League.
PCL Northwest: Portland, Tacoma, Colorado Springs, Salt Lake
PCL Southwest: Albuqerque, Tucson, Fresno, Las Vegas
PCL Northeast: Iowa, Omaha, Edmonton, Springfield
PCL Southeast: Nashville, Memphis, New Orleans, Oklahoma
IL West: Indianapolis, Columbus, Dayton, Louisville, Toledo
IL North: Buffalo, Rochester, Syracuse, Ottawa, Montreal, Pawtucket
IL East: Scranton/WB, Norfolk, Durham, Charlotte, Richmond
Now down to the AA level:
Springfield of the Texas League relocates to El Paso.
Lexington, KY and Greenville, SC (both South Atlantic League, A) upgrade to AA and both join the Southern League.
Southern League West: West Tenn, Mississippi, Huntsville, Montgomery, Mobile, Birmingham
Southern League East: Jacksonville, Chattanooga, Carolina, Greenville, Tennessee, Lexington
Texas League West: Midland, San Antonio, El Paso, Frisco
Texas League East: Corpus Christi, Arkansas, Wichita, Tulsa
No changes to the Eastern League.
The Lexington and Greenville A franchises relocate to Penscaola and Tallahassee, Florida and move to the Class A Advanced Florida State League.
Dayton's A team relocates to Bowling Green, Kentucky and remains a "standard" class A team in the Midwest League.
Evansville and Kalamazoo move from the independent Frontier League to the Midwest League, while expansion teams in Columbia (SC) and Macon (GA) join the South Atlantic League to bring A ball to 32.
Florida State League North: Pensacola, Tallahassee, Dunedin, Daytona, Clearwater, Brevard County, Tampa
Florida State League South: Lakeland, Sarasota, Fort Myers, Palm Beach, Jupiter, St. Lucie, Vero Beach
Midwest League West: Burlington, Clinton, Beloit, Cedar Rapids
Midwest League North: Quad Cities, Kane County, Peoria, Wisconsin
Midwest League South: Bowling Green, Evansville, South Bend, Fort Wayne,
Midwest League East: West Michigan, Southwest Michigan, Kalamazoo, Lansing
Sally North: Delmarva, West Virginia, Lake County, Lakewood, Hagerstown
Sally Carolina: Columbia, Charleston, Asheville, Hickory, Kannapolis, Greensboro
Sally Georgia: Savannah, Rome, Macon, Columbus, Augusta