There are a couple of things to keep in mind about your question.

First, using ball point or sharps are determined by the fabric.  For instance, you would always use a ball point needle for a knitted fabric.  Knits can unravel when using a sharp because the sharp can and will cut the thread.  A ball point 'pushes' the thread a side.  Delicate fabrics like silk will benefit as well, but you need to do a 'discovery' sew.  Take a scrap or similar fabric and test out the two to see exactly where your fabric benefits from which needle.

Secondly, felt is not a woven or knitted fabric.  Felt is usually wool, often mixed with fur or hair or with cotton, rayon, etc., the fibers being worked together by pressure, heat, chemical action, etc. instead of by weaving or knitting.  It would most likely benefit from a sharp.  But, again, your 'discovery' will tell you what is best.

Felt is forgiving.  I do a lot of my samples on it because it has a little bit of depth and stabilizing is not usually an issue.

Pat, The Avid Embroiderer