There are 3 manufacturers of Japanese cylinder beads: Toho, who refer to their product as Treasure Beads, and a second product line - the ultra-precise, ultra spendy Aiko's. Toho's are considered to be the best quality of the three manufacturers. Miyuki is second in the quality parade, and their Delica beads are practically synonymous with the term "cylinder bead" - when color numbers are given out in a bead pattern, they are almost always a Miyuki number. Matsuno, with their Dynamites, are considered a slightly lower quality than Miyuki.
Delicas come in four sizes: 15/0, 11/0, 10/0, and 8/0. They also come in a hex cut that provides extra sparkle and dimension to your beadwork. Hex Delicas are available in all four sizes, but a smaller range of colors.
Another note about colors: Miyuki rates each individual bead color as to durability and light-fastness. If you want longevity for a bead project, avoid the dyed colors and the not-so-lightfast colors. Inside dyed colors are a bit hardier than outside dyed colors, but still can show wear over the years.