Best Cutting Fluid??

Unless I'm tapping I use air. As in dry. Solid carbide end mills.

Flood Coolant: I highly recommend using a product called "TRIM C270" cutting fluid concentrate. I bought it on Amazon. Mix it with water (6 parts water to 1 part C270 for bandsaw, 4 to 1 for a lathe flood coolant system). This mix will not turn rancid, will not rust your equipment if mixed properly. About once a month, add some additional water, depending on how much you cut with the bandsaw / Lathe. About once or twice a year, add a cup of Trim C270 to the tank to compensate for loss. If you notice some rust on your tool, that means the "TRIM" is too weak in the solution. It is what they use in the local shipyard machine shop. They build ships for the United States Navy. No bad smell!