I'm a bit of a booktest nut. To name a few I have and have performed: Flashback, Ultimate Flashback, Insight, Final Exam, Unfaked BookTest, Hidden Agenda, MOAB and Double Vision. I also have quite a few force books and own Seafire but have never performed it. This is no criticism of Seafire, I have just never taken the time to put it all together. Still, I feel I've learned a lot about routining just from reading Richard's mss.
Of course, MOAB is the cleanest and consistently generates powerful responses. Combined with Busch's Mother's Home Companion it is even better.
I love Final Exam because it uses classics in literature (my wife is a high school English teacher and these are books we already had around the house)and you reveal much more than a word. The trade off is you need to know the page number but there are ways around this. Also, there is a bit of memory work involved but it isn't nearly as daunting as it appears on the first read thru. I found that I'd done about half the memory work before I even tried, simply by reading it over and recalling the mnemonic devices. Also, in pulling out your memories, you go thru a process that looks and feels like you are doing something "mentalistic" which adds to the congruency of the performance. Harvey even suggests doing it as a memory trick but I think that would be a shame as it makes for such good mentalism.
Insight also requires some memory work, but again it isn't really overwhelming. The variety of data you can reveal makes for some great presentations.
With all the above said and done, with the exception of MOAB, I am going to recommend Double Vision. We tend to like what is new (what Eugene Burger knowingly calls "the tyranny of the new" and psychologists refer to as the "recency effect") and I am doing my best to seperate myself from this sometimes insidious unconcious process.
My reasons are as follows: El Mystico included DV among his lists of tests requiring memory. Not really. At least nothing other than remembering how to do the effect which is inherent in learning any effect.
DV is like Flashback on Steroids. I always liked the Flashback principle but wished it was housed in books that didn't look cheap. I actually like the original Flashback better than the Ultimate (with the exception of the book you can use for a Hoy like test) because it is so straight forward but that is just my taste.
Putting the Flashback principle in a very nice and real looking travel book was a stroke of genius. Even mentalists who object to book tests in the first place, especially on stage, have agreed that DV makes sense and doesn't violate their sense of what is and isn't mentalism. You aren't doing a book test; you are performing mentalism around the theme of travel, which has much inherent appeal and psychological power, and using a travel guide in the process. To those who object to book tests, this makes much more sense than handing someone a book out of which they select a word or words.
And then there is the range of possibilities in DV. Sure you can reveal a word or the gist of the first couple of lines (be careful with the latter, though, because there are a couple of spots where if you follow Ecker & Berle's instructions unthinkingly you can end up in hot water) but there is so much more. You can reproduce photos, you can reveal obscure content of photos, posters and drawings, you can have the participant use a map and go on an imaginary walk and tell which ways they are turning and where they end up. The participants can select lodgings and you can tell them the name, how many stars it is rated and its phone number. You can give the population of towns, license numbers, street numbers and the time on photos of clocks. And more, but that is enough to give you a good idea of what makes this such a great booktest.
And it all follows from the basic Flashback principle (and by extension a principle that gives you all the numbers I listed above)and a few simple rules you have to memorize. You memorize rules, not facts. And the rules lead you unerringly to the facts. DV is so good it ought to be illegal.