Having a sharp needle is one of the most important factors in machine embroidery.  Note that the embroidery needle has a more elongated eye than a regular sewing needle.

Most makes of machine embroidery needles carry two main lines;  Sharp needles and Ball point needles.
  • Ball point needles penetrate between fabric fibers making marks or damage to fabrics less of a concern.  For example, a knit should have a ball point needle to prevent runs or holes in the knit.
  • Sharp point needles actually pierce or cut the fibers which can be useful for cleaner designs and less damage to textured or thicker fabrics.  Note that sharp point needles may be needed if you are using a heavier stabilizer.
  • Larger sizes indicate a larger needle tip and should therefore be used on heavier fabrics.  75/11 is suitable for most lighter weight fabrics.
Below is a guideline as to which needles to purchase for which project and/or material;

FLAT SHANK NEEDLES
15x1: HAx1, 705H   This is the standard needle with a flat shank and a regular size eye for most home sewing machines and home sewer based embroidery and quilting machines. It is widely available in a large range of sizes with a sharp or ball point, also available with PD/titanium finish.

15x1 ST: HAx1 ST, 705H-E   This is a special version of the 15x1 for embroidery and decorative stitching. It is made to higher standards for longer life. It has an oversize eye to reduce stress and tension on the thread. It also accommodates metallic threads for heavier top stitching thread and makes needle threading easier. It is available in sharp or ball point, also available with PD/titanium finish.

15x1 SP: HAx1 SP   This is a special version of the 15x1 for stretch or elastic materials and tightly woven knits. It is made to higher standards, it has a snake's head shape due to a combination of a slightly bulged eye and a slightly reduced blade above the eye.
   
HAx130EBBR:    This needle was developed for use in the new Babylock EMB6 & Brother PR-600 PR620 embroidery machines. It is an industrial quality machine embroidery needle with a flat shank, reinforced blade, light ball point and an oversize eye. It is available in a range of sizes with a hard chrome finish.

ROUND SHANK NEEDLES
DB-K5:    This needle is designed especially for industrial /commercial embroidery machines such as Tajima.
The DB-K5 needle has a one size larger eye than that found in a regular needle. Unlike sewing thread used for general apparel sewing, embroidery threads are "fluffier" and have less tensile strength. A larger needle eye, without increased blade diameter, allows the embroidery thread to pass easily through the needle's eye without fraying or snapping
   
DB-K5SS: This embroidery machine needle has all the eye features of the DBxK5, but the point has a very narrow wedge to make penetration through leather, vinyl and similar materials easier and neater.  The very narrow wedge point "slices" through the leather-like materials while making a cleanly cut needle hole. A standard "set" or "sharp" point needle punches it's way through leather like materials which may make irregularly or undesirably shaped needle holes. The very narrow wedge point "slices" through the leather like materials while making a a cleanly cut needle hole.
      
Other available wedge point needles typically have a longer wedges then the DB-K5SS embroidery needles. That's fine for most sewing operations, but in machine embroidering, the stitches are very close together, The longer wedge point needles will actually punch out the design created by those close pattern of embroidered stitches. The extra narrow wedge point of the DB-K5SS embroidery machine needle leaves enough distance between stitches in embroidered patterns to maintain the strength of the leather like material and avoid punching out the embroidered design.
   
DBxK5 Q1:  This embroidery machine needle was made for the Janome MB4 and Melco EP4 4 needle embroidery machines. It has a long extended groove, longer deeper scarf, tapered blade and a slim extra light ball point.

BALL POINT NEEDLES
Ball point needles are designed to alleviate making holes in knit or loosely woven materials. The cross fibers which constitute the knit or loosely woven materials are relatively far apart as compared to those in tightly woven materials. When a needle with a standard "set" or "sharp" point encounters one of those fibers in penetrating the fabric, it cuts right through the fiber. This creates a hole in the fabric. The ball point needle pushes aside the fiber it encounters in penetration and thereby avoids making a damaging hole in the fabric. (It is also recommended to use the thinnest possible needle for a particular fabric)

(Perfect Durability) NEEDLES PD needles have a titanium-nitride ceramic finish which makes them more wear-resistant than any other needles. When embroidering large stitch patterns or penetrating very abrasive, dense or tough materials the needle points and surface will maintain its original shape and dimensions 3 to 5 times longer. PD needle points will not wear down as fast as chromium plated needle points. The use of PD needles gives you longer needle life, fewer defects due to "dulled" needle points, and increased productivity.

WHAT NEEDLES TO USE FOR WHICH FABRIC
Canvas
 80/12 sharp
     
Lycra, Spandex
70/10, 75/11, 80/12 ball point

Coated/water proof
80/12 sharp/ball point
   
Nylon Wind breaker
70/10, 75/11, 80/12 ball point

Corduroy
65/11 sharp/ball point
   
Organza
65/9 ball point

Cotton Sheeting
70/10, 75/11, 80/12 sharp
    
Rayon
75/11 ball point

Denim
75/11 sharp
   
Satin Jacket
75/11 ball point

Dress Shirt
 70/10, 75/11, 80/12 ball point
   
 Sweater Knit
 75/11 ball point

Golf Shirt
70/10, 75/11, 80/12 ball point
   
 Sweatshirt
 70/10, 75/11, 80/12 ball point

Lace
 75/11 sharp point
    
Taffeta
 65/9 ball point

Leather
 80/12, 90/14 sharp point
     
Terry cloth towel
75/11 sharp/ball point

Lingerie & Silk
60/8, 70/10, 75/11 sharp/ball point
   
Velvet
65/9 ball point
      
* Remember when you change the needle size or the eye size of the needle, you are changing the tension on the top thread.
    * The needle size, you are changing the relationship of the needle scarf to the hook point.
    * The needle point, you are changing the way the needle penetrates the fabric.

This is not just about needles! When you change thread, backing, brand of blank product or even digitizers you may also affect the balance.

BEST ADVICE!
There is no firm, fast rule to solving problems associated with needles. Experimentation to solve problems is the best advice. Keep a variety of needle types, sizes, and finishes on hand so you will have the tools needed to solve any related problem.