Sharps are just that. Sharp... They are used for tightly woven fabric and are excellent choices for just about anything gear makers would do. The Jeans/denim needles are large sharps as they need to pierce layers of heavy fabric.
Universal points are a fairly new addition to the scene. They were designed for just about all purpose stitching. They are also the most readily available. If you were doing mass production requiring many layers of webbing I would not recommend them. But for most other uses they are completely acceptable. My own personal preference is sharps, but I usually buy universals just because I can find them easier.
Ball point are used for knit and stretch fabrics. Sharps and universals can tend to pierce and separate the fibers in the yarns. For woven fabrics that's not a big deal. For knits and stretch fabrics it can create areas prone to failure. Ball points do not pierce the yarns. Rather they tend to push the fibers out of the way. Thus resulting in fewer runs and better performance for stretch materials.
Leather needles are used exclusively for leather. Never use leather needles for any thing other than durable non-woven base materials. They have cutting edges along the shaft of the needle which is great for leather but will destroy any woven or knitted material. They are specialty needles and generally harder to find out side the craft and specialty markets.
Hope that helps.
Last edited by Ramblinrev; 11-16-2012 at 12:57..