If I had to choose one machine overall that gives me versatility, reliability, and comes at a very good price point, and most importantly has an adjustable stroke length, it would be the Biomaser. That is the one I would recommend. Mast has been my favorite for a long time, but the adjustable stroke length on Biomaser and its battery performance make it a stronger choice than Mast Tour in my experience. Most adjustable stroke machines require cam swaps, but the Biomaser allows you to adjust stroke length directly on the machine with no disassembly, which makes it much more user-friendly.

The other machines really depend on what you are looking for and what works best for you as an artist.

Artist technique
If you are heavy-handed, I recommend avoiding longer stroke machines and choosing something gentler. If you are more light-handed, machines like the Biomaser, which lets you adjust your stroke length, or the Mast Tour, are great options.

Clientele skin types
It also depends on the type of clients you work with. For example, if most of your clients are Fitzpatrick 1 or 2 and older with very delicate skin, short stroke machines that are softer on the skin will help you most. If your clients tend to have thicker or oilier skin types, then a machine with a longer stroke may be a better investment.

Final takeaway
These are simply my experiences and how each machine has worked for me, but in the end it is always a matter of personal preference. What I want to emphasize most is that it is not the machine that produces the work, it is the artist. In my opinion, technique makes up the vast majority of the outcome, tools are only a small part. And keep in mind, none of this means you cannot use a long stroke machine on delicate skin. It just may not always be the most suitable choice, especially if you have limited experience and have not yet mastered your technique and pressure. The point is not to follow this word for word, but to understand how much it depends on you, your hand, and your clients.

My explanation is meant to be educational and to help you use these machines with confidence. By putting together the specs and my thoughts, my goal is to give you information that helps you make better decisions. I would never tell students to only use one specific machine. I may recommend certain options if I notice something about your technique, but my real aim is to give you the tools and understanding to make those choices on your own, even without me being present. That is always my ultimate goal as your educator.