The B-24 had a "Davis Airfoil" wing, which was thicker, but much shorter front to back than the wing on B-17's. It was quite a bit more efficient than the B-17's, allowing more knots airspeed. The B-24 was basically 1940 technology while the B-17 was more 1935 technology. Might not seem like much, but in that era a few years made a big difference. Next time the Collings Foundation tour is near you check out the two planes side-by-side and it is obvious.
Initially the B-24 was a fine aircraft, but as they added more turrets and armor plating it grew too heavy and was hard to handle. And as mentioned earlier, the fuel system leaked. They often flew with the bomb doors cracked open to vent the interior, according to my father.
Each of the 2 4-engine bombers had their strengths and weaknesses, and supporters and detractors. The debate as to which was the better aircraft will always be argued and never settled. The B-24 was produced in greater numbers than ANY other aircraft type, however!