Good question David, in my experience it all comes down to what you’re planning on doing with your CNC.
- Bulk material removal & simple cuts: get a surfacing bit, some dado bits, and some 1/4" end mills
- Lots of plywood work: get some downcut end mills (regular ones are upcut) to avoid splintering
- Small work and engraving: you can probably stick to square or ball end 1/8" bits and smaller v-bits
- Sign making: most of the time a 1/4" v-bit and end mill is all you need
- Intricate contour and relief cuts (3D carving): look into getting ball or tapered end mills
- Metal cutting: pick up some reasonable 1-flute cutters, larger diameter = less likely to break
Most general purpose bits should have 2 flutes. We’ve got a guide on teaching the lingo and some other recommendations here: https://sienci.com/mill-one-resources/cutting-tool-guide/.
As far as brands are concerned, I’ve mostly stayed away from any particular type. This is because at the start any beginner is likely to break some bits here and there, so it’s easier to start with the cheaper no-name brand stuff.
If you’re working your way up, I’ve had a reasonable experience with Freud router bits, and we also are starting to stock more router bits on our online store as well. Our most recent batch has been all custom made to our own specs so that we can optimize the bits to be used on a CNC router. They’re nearly ready to be put up on our store, you’ll find them here: https://sienci.com/product-category/cutting-tools/ There are many more online sources including ebay and amazon for a variety of bits, common hardware store router bits also do the trick just fine.