You need a blunt needle usually referred to as a tapestry needle for cross stitch as we part the threads of our linen rather than pierce them.
The size of your needle depends on the count of the fabric you are using. There are several different brands and sizes available. The higher the number the finer the needle.
As a general guide use a:-
Size 18 needle for 6 count aida
Size 20 needle for 8 count aida
Size 22 needle for 22-25-27 count even weave linen, 11 count aida
Size 24 needle for 32 count even weave linen, 14 count aida
Size 26 needle for 32 count even weave linen, 16 count aida
Size 28 needle for 36-40 count linen, 18 and 20 count aida
For higher counts you may like to try a size 10 beading needle.
Brands vary in quality and some are better than others. Most needles are nickel plated. Gold and platinum plated needles are available and are less prone to rusting and slide through fabric easily.
Never leave a needle parked in your fabric for long periods of time to avoid rust spots and marking your fabric.
Whilst stitching a needle minder is useful. They are made from two magnets, one for each side of the fabric. The tops are decorative and collecting them can become addictive. You can drop needles onto them and they will stay even when you turn your fabric over.
It is recommended to replace your needle with each new project as old needles with rough areas can damage your work. A strawberry emery will help keep your needle in tip top condition.
If you are interested in how needles and pins are manufactured CLICK HERE