B-26 is fine, if you only need a medium bomb load and plan to stay low, under 5K AGL really. Lower even to help prevent enemy fighters coming at you from directly below you where you've no turret coverage. The ammo load of the rear gun is nice to have. I don't take B-26's very high, ever.
B-17's at 20 to 25K is where I generally operate if using buffs to pork strats. Bombers can be very accurate at those heights... I've been loading 500 lb bombs, and taking out strats with salvo 1.... but I do it by adjusting my throttle to where the B-17 stays at constant altitude. Tried using trim to level it out, but at full throttle, the B-17 still wants to climb.... which throws off a long 15 to 30 second calibration. So, I give up some speed for high accuracy at those altitudes.
I think in-game, we are missing a dorsal gun for the B-17's Radio Operator, aren't we?
Used to run B-17 at 25 to 30K to pork troops.... but with so many barracks per field now, I don't run those missions any more. Resup happens too fast, and fewer planes come clawing up to those altitudes to attack me..... which was part of the fun.... especially when it was an La7 or Niki trying to climb up after me.
I'll attack CV's with Ar-234's and Ki-67's at between 5 and 7K altitudes. I take hits, but the speed on the way in, and shorter drop time, helps against maneuvering CV's.