The Blue Book has become the industry standard reference, so I'd go with that.
Most of the time, that's the book a dealer or collector will pull out to check prices.
It also tends to be a little more exact then the other books "Good, Very good, Excellent" ratings. Since the Blue Book goes by condition of original finish, it gives a closer valuation.
The reasons for the difference in prices in the books and at the gun show is the books have at least one year publisher's lead time, and I suspect the book editors only go to the big gun shows, where prices may tend to be a little lower.
In all cases, it's hard to keep up with a rapidly changing market, especially when dealing with skyrocketing gun prices on items like Colt revolvers, and US military issue guns.