B-17 vs B-24 is a choice I make depending upon mission.  
B-17 is definitely much more durable, and I get a lot more fighter kills in it.  If I'm running bombs into an airfield with a lot of enemy around, give me a B-17 anytime.  It takes a licking and keeps on ticking (and shooting back at you).
B-24 is great for CV killing - it'll hold together while I come in on a shallow dive at 300 Kts IAS, pull up and then dump bombs all over the enemy CV.  It has a better bombload, and slightly greater level speed, but a few hits in the wings and it  burns like it is filled with gasoline-soaked rags.  
All in all, I'd take the 17 if you are going into a fight and want to get home alive, or at least take some of the b..tards with you.  Take the 24 if you are going on a suicidal dive bombing CV killing frenzy, or if you have some escort.
EagleDNY
$.02
