I have built the jig that cuts the tenon on the end of the neck, and am thinking about the jig that cuts the mortise on the end of the body. It seems to me that getting a tight fit directly off the jig will be hard, so I wanted to ask - how close is appropriate "off the jig"? Do you expect to fit with lots of hand work, some minor handwork, or do you plan to have it fit right from the start, because you set up your router right, your jigs are right, and you are a god (goddess) of the router?
It seems to me that even with jigs that are extremely accurate, the actual width of the tenon/mortise AS CUT will be very dependent on depth of cut - the bit is tapered, so a few thousands of an inch more or less stickout will affect the width of the cut. This will make repeatability very hard, since it's hard to set up the router bit the same way every time, and you could use depth of cut of the mortise (which is less sensitive than the depth of the tenon, since it has to be deeper by some amount around .050" to .100", as I understand it) to minutely adjust the tension of the fit as long as you did iterative test cuts on scrap.
Anyway, since this is school-time for me I appreciate any and all advice. This is really an exercise in learning how to do this type of joint with routers and jigs, so not really a "which neck joint is best" kind of deal.
