Like Des, it kind of depends on the model. Sticking to WWI, I've mostly built Roden kits, and due to their, well, challenging fit, I find it quite hard to pre-paint a lot and assembly it afterwards. On the Fokker D.VII 1/72 I'm currently building I've pretty much assembled the whole airframe, wings/tail included, and only need to fit the top wing, undercarriage and some detail parts later, due to it's less than steller fit.
On the other hand, the Albatros I'm building at the same time fits better, so I've only put the tailplanes on and will do the wings later.
How I work also depends on the colour scheme; I'm doing Jasta Raben now, so it's not much of a problem to assemble all tail parts, as everything will be white.
When these models are done I'm starting my WnW Fokker DVII, which will probably be a whole lot different to build, and will probably lean more firmly towards option #3!
Jeroen