Have never bothered to look at the Fujimi kit so have no comment regarding that one.
I have built six of the Hasegawa A/C versions and am working on another two. Also have built two of the Super Bugs.
The Hasegawa kit does have some assembly problems to overcome, but if you are careful during the assembly, you can overcome most of the fit problems.
Most of the major fit problems are the aft fuselage top to bottom fit just behind the wing, and the intakes. By working the areas carefully with some trial fitting before gluing it together you can get it to go together OK. Then a little filling and sanding will take care of the rest. Most bugs have the "NAVY" and carrier designations, as well as the slime lights in this area so losing some scribed detail is not a big deal.
The intakes will fit if the sides of the intakes/fuselage are aligned and glued carefully. As with the aft fuselage, a bit of feeling it out and careful trial fitting goes a long way toward a good fit. But be prepared to use some putty here and there.
Final complaint for me was the diagonal seam between the top and bottom of the nose pieces. It goes through an area that really should be pretty smooth and clean. This usually means some minor rescribing after assembly.
The rest is just normal stuff with any kit. I would also suggest replacing the kit seat with something more detailed.
And oh yeah, Be sure to drill out the holes for the fences BEFORE you glue the tops and bottom of the fuselage together. Otherwise it is a really fun time detecting where those damn holes are.
It is not the perfect kit. Assembly is more complex than some other kits, but when done it looks accurate to me. I intend to build at least another dozen or so. Too many very neat color schemes not to be building them.
Norm