Above you'll see the Nugget TD in white, layered on top of the Original Nugget (grey outline.) The Nugget TD has a slightly pulled in nose, and more notably a drastically pulled in tail compared to the original Nugget. It also has a touch more rocker in the nose and tail. Narrowing the tail through the back half of the Nugget TD does a few things: speed maintenance is a huge advantage in better waves- Less surface area in the tail equates to less planing speed and more drive, so your more pulled in tail is going to act as an anchor at high speeds and steep critical sections. Another benefit to the narrower tail is that it creates a tighter turning radius when coupled with a bit more tail rocker. The wider tail of the Original Nugget does the opposite, it generates speed naturally, and it will be a bit looser, more forgiving and generally easier to surf.
The Nugget TD excels in punchy surf, or bigger more powerful conditions.
The Original Nugget excels in sloppy, small and weak conditions- but isn't limited to less than ideal surf- it still goes quite well in better waves.
Both versions of the Nugget have a large overlap- they both work well in surf up to 8 foot (faces) or so, the Nugget will cover the smaller end better, and the Nugget TD will cover the bigger end.