The upside of the SB800 is that it is small = portable, built in fresnel lens = a certain amount of beam focusing, fits in a hot shoe, works off camera as well and most importantly works with the Nikon Creative Lighting System, so it can be optically fired from another strobe while still using TTL metering.
The downside of the SB800 is that it is small = not as powerful as some other larger strobes, built in fresnel lens = no bare bulb and no on strobe modifiers.
So, it really depends on what you are planning on shooting. If you want something small and lightweight for doing events, then you probably want an SB800. If you want to do a lot of studio work, then you probably want something larger like an AB800.
In fact, you can cook a speedlight with almost any external power pack.
