I use about half thin, half medium. Like Minnflyer says, thin CA is applied with the pieces in place (just a drop or two will completely soak the joint) and medium CA is applied to the pieces before you stick them together. You get maybe five seconds to position the pieces correctly, so pre-fit the parts dry.

The decision to use thin versus medium depends on how tight the joint is. Thin CA needs a very tight joint, like wing ribs to slotted LEs and TEs, and doublers. Less well-fitting joints, like cross-bracing in control surfaces (yes, I am too lazy to get a perfect fit), I go with medium. Sometimes I'll "fillet" thin CA joints with medium CA later on.

I use AR once in a great while. I'd use it more, esp. for sheeting, if I had the patience.

I use epoxy when I need more than 5 seconds to fit the pieces, like attaching tail feathers.