Below are some stats for Boston, JT. As for working fires (a term no longer used by the BFD), its pretty spread out across the city. Companies in Beantown see work, but nothing like 30-40 years ago.
Ladder's 3 and 10, the BFD's two tower ladders (or Tower Companies as they are referred to by the BFD), respond to all confirmed fires in their respective division as the 4th due Truck Co.'s on the box, thus these companies tend to see a lot of work. Tower Ladder 3 is in Division 1, and Tower Ladder 10 is in Division 2. Generally speaking, Engine 37/Ladder 26 and Engine 33/Ladder 15 have consistently been busy houses for fire duty, as have Engine 24/Ladder 23, Engine 52/Ladder 29, Engine 53/Ladder 16, Engine 7/Ladder 17, and Engine 21.
Below are the companies, districts, and houses that usually make the top 5 for runs.
Top 5 Busiest Engines (upwards of 2,500-3,500 runs annually):
E21
E37
E33
E7
E14
Top 5 Busiest Ladders (upwards of 2,500-3,500 runs annually):
L26
L17
L16
L23
L6
Top 5 Fire Districts (For total number of incidents within each District):
D4 (Back Bay, South End)
D7 (Roxbury, Dorchester)
D9 (Roxbury, West Roxbury, Jamaica Plain)
D3 (West End, North End, Charlestown)
D8 (Dorchester, Mattapan)
Top 5 Busiest Firehouses (For total number of responses per firehouse):
E37/L26 (Roxbury, Fenway)
E7/L17 (Back Bay)
E33/L15 (Back Bay)
E53/L16 (Roslindale)
E24/L23 (Roxbury, Dorchester)