I believe that the best way to bind a grimoire is through the screw post system. This binding style allows one to move pages around without having to take the whole book apart, which is ideal for those who prefer to print out pages or draw artwork in the book. This is an especially good advantage with larger tomes that would be hard to work in without the advantage of removing pages. Unfortunately, it isn't quite as strong as a traditionally bound book, but it still serves its purpose tremendously well. The pages of this style will always lie flat, which is a great advantage. Another advantage of this system is that if the number of pages outgrow their binding, you can add an extension to the screw posts and make a new back piece. Of course, it is better to create the book to allow more room than you think you need, and put blank pages in the back to hold the shape. Also, one should not make a book too thick, as the thicker the book becomes, the weaker the spine will be, no matter what binding style is used.
Coming in at second place is the traditional binding system, sometimes called perfect binding, which is the most durable and beautiful style. The folios, or signatures, are sewn to a backing cloth, usually linen, and the cloth is sewn at the sides to the spine. What this allows is for the book to lie flat without damaging the signatures. If you look at a well bound book from the top when it is opened, you will see that the backs of the pages bend upward, allowing the book to stay open. This style is particularly sturdy due to the fact that the pages are sewn together, and they have no holes that can rip and tear. If you drop the book, it is less likely to be damaged than a post bound book. However, there are plenty of disadvantages to traditional bindings too. The first and foremost being that the pages are not removable. You cannot print out the pages, and so are forced to hand write them. If you spill ink, make a mistake or simply wish to remove the page . . . too bad. Technically you can remove the pages, but that feat takes skill, time, and patience.
There are other styles of binding as well, but not many of them suit grimories very well, especially if the book is more than an inch thick, which of course is common for grimories. Case binding is similar to perfect binding, but the pages cannot bend out, and so it is much easier to damage the spine and the pages often will not lie flat. In fact, it is common for this binding style to only open halfway, forcing the reader to hold one of the sides straight up, while the other side lies flat. Of course, hand writing in a style like this is practically impossible.
Styles such as comb binding, spiral binding and ring binding are practical in the early stages of grimoire development (mine is still in a three inch binder, eagerly awaiting its new home), but is very impractical in the long run. Three ring binding is weak, and pages will often tear out due to the loose binding. Comb binding allows the pages to lie completely flat, but is very weak for large amounts of paper, and pages are not easily removed. Spiral binding would allow you to remove pages, but with some difficulty, and again is no good for large amounts of paper. Here is a link to a page that illustrates different styles of binding.
And for now, ttfn!