Psycho:
I've built Hasegawa and Academy B-17's and Academy's B-24's. Building is pretty straight forward, but I'd advise test fitting the pieces as you build, since sometimes they don't quite fit and need a little filing and sanding, especially to get the fuselage to close around all the bulkheads and turret rings.
For B-17's, I'd say that Hasegawa's are less "fiddly," but they don't seem to be in production run right now. Academy's (reboxed by Airfix) require you to cut out the starboard waist windows, depending on the version you choose to build.
Hasegawa's B-17F can only be built as an early model, since it doesn't have an astrodome over the nose. Academy's B-17F can be built as a later model, since it does have the astrodome. The dihedral on the Academy's wings seems a bit overstated, also.
The Academy/Airfix release B-17G can be built with open bomb bay and some versions have a choice of tail turrets.
One thing I do remember about the two Liberators I built is that, once assembled (top and bottom), the wings don't fit into the fuselage very well without some sanding to thin them down. It's also difficult to find a way to weight the nose so the plane rests on its tricycle landing gear. I just drilled a hole in the back somewhere and glued in a straight pin to keep it from settling to the rear. Otherwise, Academy's Liberators build up pretty well.
I posted a few pictures of a couple of my Fortresses in some threads here, so if you do a search maybe you can find them. I posted my "Memphis Belle" earlier in this thread.
In summary, either the Hasegawa or Academy/Airfix planes are all pretty nice. Revell's older B-17 is quite old and shows its age, with lots of raised rivets and movable control surfaces and poor renditions of windows. I think Revell Germany recently re-released it, but it dates back to the middle 1960's, and is much inferior to more contemporary versions.
I have not built Hasegawa's newer B-24, since I think they're a bit pricey, and the Academy Liberators are cheaper and look just fine.