A10......forgive me if I'm oversimplifying the answer to your question. It's early, and my brain is not quite working yet.

'CA' is an abbreviation for 'cyanoacrylate ester'.
Commonly known under the trade name of 'Super Glue' to most non-hobby enthusists. "Super Glue" is a pretty generic, low quality type product, but chemically the same as what we use in our little hobby here.
It comes in a number of formulations, from a thin type, which wicks into pourous materials, and dries quickly, to a thick, nearly gel like formulation, which is VERY strong, and takes a few moments to cure, and a few types in between.
This adhesive is used in numerous ways......the folks that posted before me have kindly pointed many of them out.

Epoxy refers to any number of catalyst type adhesives that use a mix of a hardner agent, and a resin agent. When mixed together, a catalyst reaction takes place (you can feel the heat given off by this reaction...try holding your mixing cup in your hand after mixing up a batch), and the mixture begins to solidify. Many applications for this type of adhesive; fuse to bulkhead joints, applying fiberglass cloth to , say, a wing, to name a few.

Both products have many applications in our hobby, and I'm sure you have used both for many of them.

I think many would agree, but I believe the 'ZAP' line of CA products are the best ones out there.

Brg,
Jeff