Liz,
You are right about it being hard to learn about all the skillet handles from photos, especially if only one side is shown.
I have yet to master my digital camera or get the time to do it. Plus I have few Griswold skillets any more. Any chance you will make it to our convention this year? If so I'd be happy to discuss this complicated subject in detail. Looking at many thousands of pans over 30 years has given me and other old time collectors a knowledge of some of the smaller details and aspects of iron cookware. It is really hard to cover the subject without a lot of work and time. At the convention there are thousands of pans to look at which makes comparing so easy.
I think you can find more information from the red and blue books if you go back and look over the handles and photos some more together with the dating on the pictures (which isn't always too close but we don't always know the dates real close).
As to which are the best or more in demand to collect, sometimes you can tell by the prices with the higher prices being the rarer or more in demand. And much depends on what YOU like. I disregard values when collecting and get what I like whether it is rare and valueable or common and cheap. It's the quality and style of a piece that appeals to me regardless of the make or demand. For the makes covered, the red and blue books do give approximate dates for the various skillets. One maker's handles will not always mimic another makers pans as all had their own ideas of what a handle or pan should look like. I do find the Griswold handles to be more pleasing than most makes.
Steve