"Best" depends on what you are planning to sell, where you are, and what your budget is.
You will have an easier start with a Brother 6 needle machine (PR series). Usually they come with software. The PR-650 is the newest one, but many people make good money with the older versions (PR-600, PR-600II, PR-620).
If you are going straight to a commercial machine, you will be satisfied with a Tajima or a Barudan. Melco works well for a lot of people. I suggest taking a few hours and reading this forum in depth. After all you are about to spend something between $5000 and $20,000, so that seems like a minimal investment of time.
As with most things in life, the answer to your question depends on what you are planning to do, your budget, availability of local sales and service.
Good luck.