That's a tough one. I'll use the definition of complex (my guess) as referring to the number of steps, number of parts, and time involved. Not poor fit, inscrutible instructions or the need for more than the usual outside research.
I recently built a model Italeri 1/9 scale Norton 750 Commando motorcycle kit.
It came out well IMO, and there was only a small amount of lack of clarity in the instructions.
Complexity factors;
A lot of parts in several different materials- styrene, rubber, metal.
The need to pre-paint most all of the parts prior to assembly.
Assembly a combination of adhesives, mechanical and interference fit.
Movable parts including steering, front and rear suspension and turning wheels (rear when the chain isn't fit onto the sprocket.)
Extreme delicacy in the assembled model.
I really liked it.
The Revell 1/144 Flower Class Corvette. I'm working on it in stages, as it has a really complex set of aftermarket PE. Not the kit's fault. I'm also backdating it to an earlier short forecastle ship. The subject is the fictitious "Compass Rose" from the novel The Cruel Sea.
75 PE parts on the engine skylight (except several brass wire parts I had to make for ones that the floor stole).
Some yerars ago for the FSM Aeroplane GB. Roden 1/72 Felixstowe.
