Ask what are the best felting needles and you will get a different answer from most people.
It really is personal preference I think. What one person has said are excellent needles I haven't got on with at all. Felting needles have changed a lot since I started felting and there are so many different kinds and gauges available for needle felting now. I will tell you about some of the needles I use and welcome comments from you to share your favourites too.
You can buy triangle felting needles on Amazon or Ebay that are just sold as 3 different sizes, usually course, medium and fine. They arrive in a tube with no labels or information usually. If you get these when you are starting out because they are cheaper and you may break more needles it is fine. It is all we had to choose from many years ago. I find that they work well and I buy them for my workshops as people often break needles and it can get expensive to keep replacing. Also they are taken home at the end of the workshops as it is not good practice to use the same needles at another workshop. If you are not given clean needles or you are asked to hand them back in at the end of a workshop I would be asking questions. Unless someone has a medical autoclave they will not be sterile when reused. You will notice that the needles are different lengths if you get these. Usually the course is the longest and the shortest is the fine one. You would start your creation with the course one, as the wool compacts you will notice it gets more difficult to use that needle so move down to the medium. The fine one is used for attaching embellishments and smoothing the felt at the end.
Triangle needles as the name suggests have 3 sides with barbs on each side, you can also get star needles with 4 sides which I love as they are faster to felt. I generally start with a 38 star needle for the core, you can use a 36 star but I personally do not like the feel of it. I then move on to a 40 gauge twisted needle as it starts to firm up and tidy the surface up. But the fine or 40 gauge triangle needles work just as well.
You can also buy a reverse needle. This has the barbs going the opposite way so once your felt is lovely and solid and smooth you can pull the wool back out leaving a lovely fluffy texture.
These are the ones I use the most, I tend to use a single needle unless I am creating something much larger and will use a multi tool then. I have the pen style tool that holds 3 needles but I take one out and work with 2.
I could go into more detail but Heidi Feathers has a very good guide to needles on her website which can be found here.
I buy needles from Heidi Feathers, The Makerss and Wingham Wool mostly.
The needles are delicate and will break easily if not used correctly. Remember the higher the gauge the finer the needle.
Check out my tips for advice on using needles.