Re: B-17, B-24, B-29, or Lancaster?
While I'll agree on the Avro, BH, where did you get the idea a howitzer was mounted in the nose of a Mitchell ?
The Avro was the champeen heavy weight lifter of WW2 bombers toting first Barnes-Wallis' "Tallboy" and later his "Grand Slam" to sufficient altitude to perform as advertised. No U.S. bomber in the ETO could do so. Sub pens at Brest and Lorient, rocket and super gun sites in northern France, and the Tirpitz and the Bienville viaduct all fell victim to this superb combination. What the Avro lacked was defensive firepower and armour.
The B-29 was the "next generation" of bomber and performed excellently under severe conditions at extreme ranges enabling us to hold much of Japan's home islands at risk.
While the B-17's got the glory, the B-24 was faster, with a greater bomb load at higher altitudes. Just fewer of them. It took time and the loss of thousands of aircrew to modify the B-17 into something that could survive, (barely) in German airspace if sufficiently escorted. Since these models appeared around the time long range escorts appeared and the decline in pilot skill in the Luftwaffe were also occurring I suspect any "opinion" has to remain more that than established fact. >MW