The Barbara Walker treasuries are actually four books, each a little different. If I could have only one, I'd get the Second Treasury.
It's almost twice the size of #1 and I think there's much more variety, especially in the lace stitches. The directions for each stitch are written out, not charted, if that's a problem for you. The third Treasury is all charted. The fourth, to me, is the least valuable; only get it if you want to round out the collection. It seems to have a lot of miscellany and afterthoughts.
This is an interesting site on which volunteers are posting full-color swatches of Walker's stitch patterns to make up for the one big complaint some people have about her books: the black-and-white pictures. http://thewalkertreasury.wordpress.com/