We all know that all files are not created equal. We all have our perfect file that we like to use and there is absolutely a good reason...Because we do.
I personally prefer a Zebra Half Moon file for all of my work. My Favourite file in our shop is the 120/150 grit. I find that a Zebra file is more efficient, operates smoother and lasts longer than traditional white files. I started using this shape about 15 years ago and have never looked back. It has a straight edge that is perfect for lower arches, sidewalls and squaring up the free edge. The curved part fits the cuticle ever so nicely and reduces my chances of taking a piece out of my client. The 120 side is the perfect grit for reducing free edges, working out lifts, and refining if I have a bad day sculpting. The 150 side is great for smoothing things over and won't leave my surface too smooth so that I have issues with things sticking when I am doing acrylic. I still do some of my prep with my hand file, so the 150 comes in handy for this too.
I also prefer a more expensive file over a disposable file, let me tell you why. A long time ago when I started, disposable files weren't really a thing. Us techs paid top dollar for our files because they were durable and lasted a long time. These files are still made relatively the same. They have a nice stiff core (so important for straight sidewalls and lower arches), premium paper and grit too. The premium paper and grits that you find in a branded file, last much longer than off brands and way longer than a disposable file. The edges are more refined and softer, meaning that even if you forget to season your file your chance of cutting someone is reduced because the edges are more aligned with the core and little chance of overlap. Branded files also don't leave behind little specks of grit to mess with your eyes or make you crazy. Often a disposable file the grit kind of just falls off and it doesn't feel sharp.
I also prefer a more expensive file because I am used to reusing my files. When I am paying what I pay for my preferred file, I want to get the most out of it. You can freak out if you want to... I'm used to it, I can take it. I know that in some places it is illegal to reuse items that are deemed disposable by a governing board. In that case, definitely don't choose a reusable file, stick to the toss away files. OR choose a reusable file and build it into your service costs, and only use it once. Keep in mind that I only do myself and family, and the files are properly cleaned and sanitized in between each of my services, should I cut someone, the file goes in the garbage. Remember that we all are subject to different rules, stay in your own lane and follow the rules set out by your governing body, the way your were taught by your educator, or the way you feel most safe.
On that happy note, DID YOU KNOW that the files that come individually wrapped, are no more sterile or safe than a file that comes in a 50pk? They are all made on the same production line, not at all a sterile environment. Technically we should all be giving our files a wash and spray before touching clients with them, most don't...but we should.
Over the years in my career I have switched the grits on my files, but never the type of paper. I moved away from the white and black files and the square shape as soon as I was finished my training. In no way do I think you should toss all of those files out if you love them! Nor do I think you should change your shape if you love working with it. This is just an opinion piece. Use what you love.
My early training had me using a 100/100 white jumbo square file, this bad boy was HUGE and toothy to start, but only lasted a couple sets or fills before it needed to be replaced. Now, this might be because my sculpting skills in the start were, lets say, not super awesome. 20years ago I was paying $3/file, this expense is what led me to seek out the best file for me. I spent about a year looking before I settled on a branded file that I loved and would last me 10ish sets