After graduation you will either go to an AEGD/GPR or direct assignment (, Green side orders (Marines: here or overseas) or Blue side orders (Navy: ship, shore, or overseas).
I recommend an AEGD/GPR. You have time to build your speed up and you get used to military protocol (chits, leave, Fitreps, etiquete, etc...) as well as rotate through many of the specialties and finish with a certificate (and don't forget the 250 CE credits towards your FAGD!). If you go directly to an assignment you'll probably end up with the Marines or ship but most likely at one of the recruit centers (Marine or Navy boot camps) so you can learn the ropes and pick up your speed.
No matter what you decide, the Navy detailer will have you fill out a wish list of choices where you want to go. You may want to discuss this with him.
Just to give you a heads up, there's lots of billets opening up for the 1st, 2nd and 3rd Dental Battalions as well as for many of the ships in the fleet. Because of the war on terror, your opportunies to deploy are very high no matter where you go.