Comparing the staff and wand are like comparing the fork to the spoon. They serve different purposes, even if they are both used in the same setting/context. Wands help to channel, amplify, and direct energy, while staffs/staves are you used for cleansing and banishing of negative energy. They do correspond in their use for drawing symbols (runes, sigils, pictures, etc.) in the ground or in the air. They also both correspond with fire. So as to which is better? It really depends on what you are using it for.
Since everyone else already explained the difference between the 2, as well as stated how they are similar, I will merely suggest that you use whichever one you are more comfortable with.
In my opinion I would also say that they both have a purpose, and they are both very convenient tools. If you don't want to pick one, perhaps get both. If you already have a staff, go out, find a branch and carve yourself a wand, or vice versa :)