Most needlepoint artists use a Tapestry Needle for working a canvas. Tapestry needles have a dull point, making it easier to slip the needle through a hole in the needlepoint canvas without catching or splitting the warp or weft threads of the canvas.
The size of the needle depends entirely on the size of the mesh of the needlepoint canvas.
For example, a narrow needle should be used on fine-mesh canvas, while a thicker needle is used on canvases with larger hole sizes.
Chenille needles, which are similar to tapestry needles can also be used, but these have a sharper point and larger eye, and are generally better suited to other types of embroidery.
When purchasing needles, a good rule of thumb to remember is that the higher the needle number, the finer the needle. A general guide is shown below, but it is also good to test your needle on an inconspicuous corner of your canvas. This way you will make certain that your needle will pass through the canvas without much abrasion, and carry the thread through easily, avoiding wear on the thread as you stitch.
Selecting a Needle for Needlepoint
08-10 Mesh Canvas - use a size 16 tapestry needle10-12 Mesh Canvas - use a size 18 tapestry needle
12-14 Mesh Canvas - use a size 20 tapestry needle
16-18 mesh canvas - use a size 22 tapestry needle
DMC Threads and Susan Bates have both prepared a guide for selecting a needle based on the type of project and thread used.