Hey, I have some of my grandmother’s set from 1925. If you can get some good ones from that time, I’d suggest either from the 20’s or 30’s. I also have have a set from 71 and, though I’m happy I have it for $10, I’m still trying to gatehr together another set to complete my grandmother’s-using ones from the 20’s and 30’s. I have some from both and the illustrations are lovely-the 71 ones aren’t as lovely; more “printed-like” and has less of that hand-drawn look.
Dover has started reprinting some, though I don’t know if they are hardback or not. I think they are based on the 1935/1937 version?. The harder ones to find: In the Nursery and Storytime.
http://store.doverpublications.com/0486499065.html#ReviewHeader
Also, here’s some info: http://www.valerieslivingbooks.info/mbh.htm