Microtex: Microtex are also sometimes called sharps. They’re perfect for neat piecing because they are sharp. I typically piece with a 70 or occasionally an 80. I also sometimes quilt with a Microtex 90.
Quilting: I use these for quilting (shocking I know!). They’re designed to go through multiple layers. I find the tension is usually magically perfect when I use these. I prefer the smaller size 75 because I use a relatively thin batting.
Jeans: I use these almost anytime I have something with interfacing. They’re designed to prevent breaking when sewing through difficult substrates like denim. I love that they rarely break! I use all the various sizes depending on how thick the interfacing and thread I’m using is.
Leather: If you’re stitching through leather, these are the best. The needle pierces a hole in the leather for smoother stitching. Because of the piercing nature, these needles aren’t always perfect for synthetic leather because it can cause ripping. I always do a test.
Ball Point: This is mostly when I’m in garment sewing land. It can also be called Jersey. These are perfect for stitching with knits. I use assorted sizes depending on the thickness of the knits.
One needle that I get a lot of questions on that is notably missing from my list is the Universal. Universal needles are part ball point and part sharp. I find they don’t do either job particularly well. Would I use one if that’s all I had? Absolutely. Do I buy them regularly? No. They’re universally not that great because they’re trying to do two jobs. I prefer to use a Ball Point when I need it or a Microtex when I need it.