I don't think there is a lot to differentiate between these three bombers. If we look at the raw data, it is apparent that they are very similar and that the mix of crew, defensive armament, and mission being the variable.
Empty weight (lbs)
B-17 36,135
B-24 36,500
Lanc 36,828
Normalizing empty weight based on Lanc configuration of 7 crew (one pilot) compared to 10 crew for B-17/24 and two pilots, 8x.303 Browning MGs vs. 10x.50cal Browning MGs, and three turrets vs. four.
MGs 422 lbs
Ammo (two additional guns) 330 lbs *
Crew (three with added support facilities) 700 lbs
Ball Turret 500 lbs (?)
Additional crew station 200lbs (?)
Total delta weight 2151 lbs.
*Assuming .30 and .50 cal ammo weighs the same-a faulty assumption.
(?) indicates WAG
Corrected empty weight (lbs)
B-17 33984
B-24 34349
Max weight (lbs)
B-17 65,500
B-24 65,000
Lanc 68,000
Max load carrying capacity (lbs)
B-17 31516
B-24 30651
Lanc 31172
Max load carrying capacity is awash
Max A/S (mph)
B-17 287
B-24 290
Lanc 280
Max A/S is awash
Ceiling (ft)
B-17 35k
B-24 28k
Lanc 24k
Significant survivability edge for the B-17, but lower target strike accuracy
Cruise Speed (mph)
B-17 182
B-24 215
Lanc 200
Cruise speed adds to survivability by reducing ingress and egress exposure to threat. B-17 is at a disadvantage here.
The B-17 has a reputation of being a strong and survivable airframe.
Total Power (Hp)
B-17 4800
B-24 4800
Lanc 5120
Horsepower favors the Lanc but does not seem to translate to superior performance.
Range is difficult since, for bombers, it is a trade-off between load and fuel. Range is a combination of aerodynamic efficiency and engine efficiency. The B-17 looks more an airplane than the other two that look more like a freight train. However, the B-24 has a more advanced wing. The liquid cooled engines of the Lanc probably reduce frontal area but none of these aircraft can be called clean. Also, I suspect the Merlins are more efficient than the radials.
Due to the liquid cooled engines, maintenance was probably higher on the Lanc.
Other factors include physical bomb carrying adaptability. The Lanc seems to have an advantage here, followed by the B-24.
All in all, as I have said, there is not a lot of difference here. Any of the three aircraft, configured correctly, could perform the other aircraft's tasks with negligible effectivity change, except for a few discrete missions, where the Lanc has an edge.