I have three sets that I bought over the years (and one that I sold)
1961 Games Research, with wooden pieces
1985 Avalon Hill "bookcase" edition, with plastic stars & anchors
1992 Avalon Hill "deluxe diplomacy", wooden blocks with flag stickers (sold years ago, stupidly!)
1999 Hasbro, with the metal pieces and SC markers
Oddly enough, I like the 1985 edition. Why, because the stars and anchors don't take up as much space and obscure the province names, particularly when you take over smaller ones. Even though I know the names of all of the provinces, I think it looks easier to see. Some people refuse to play with plastic pieces but if you're playing with less experienced players, or they haven't played in a while, it helps to be able to see the names. Wooden blocks, or the cast-iron pieces, cover them up, even if they do look nice. However, I wish it came with more pieces for each player so you don't have to borrow from a defeated power later in the game. Of course, I've never survived that long...