The best lenses for photographing the Milky Way are fast wide-angles. By “fast” I mean a lens with an f-stop of f2.8 or lower. You can get away with an f4 lens, but an f2.8 lens is better. Every full stop down collects twice as much light as the previous stop. So an f2.8 lens will collect twice as much light as an f4 lens. This means you can use a lower iso, which means less noise. It also mean you can opt for a shorter shutter speed, which means less streaking of the stars.
A wide-angle lens will let you capture more of the sky and include foreground elements for a better composition. For full-frame cameras, stick with 24mm or less. You can get nice shots with longer focal lengths, especially if you shoot to stitch a panoramic, but 24mm or less will generally give you the most pleasing single-shot results.
For APS-C cameras, stick in the 10-16mm range. This will give you the full-frame equivalent of roughly 15-24mm.