Well that is a loaded question. You don't think there is just one answer to that do you Really, it all depends on what you are looking for and how much work you are willing to put into it. The key to a show car quality finish is PREP WORK. There is absolutely no wax or polymer out there that is going to make paint in poor condition look new again.
I have tried a lot of products, carnauba waxes to polymer sealants from just about every vendor that you will see people recommend here. I always keep coming back to Meguiars. My personal favorite combo is Meguiars #9 swirl mark remover for regular surface prep, #7 show car glaze for the deep wet appearance and then topped with #26 high tech yellow wax. I have been using this sytem for years and have yet to find anything I like better. It gives my Laser Red paint a deep, dark, wet look that I really like.
Meguiars is coming out with a new consumer product line that was announced at the 2003 SEMA show. It is a line of pure polumer products that I am definitely going to be trying when they become available in stores come February. You can find multiple threads on the product by going to www.autopia.org or www.showcargarage.com and doing a search for "tech wax" or "nxt".
Judge for yourself, these are pics of my '01 GT after #9,#7,#26.
After all the prep work that was mentioned above, Zano Brothers showcar polish is unbelievable. It is only available by mail order or internet (http://www.miata.net/products/body/zano.html).
It gets better the more you use it. The paint somehow absorbs the stuff and and builds and builds. By far the best finish I have ever used. You must first prep the paint by other methods which they also offer.