Hi Rob - the “best” place is really a matter of opinion. Starting out, recommend getting relatively less expensive bits from eBay - they are still good quality and if you break a few, not a big loss of money. As you progress, I would recommend Amana bits over all else. They seem to hold their edge best for me; however, they are perhaps some of the most expensive. I get most my bit from bits & bits or tools today. You can the same bits from Amazon too as it goes back to the company for fulfillment; link to my full cost spreadsheet here from my digital manufacturing series..
I would be remiss if I didn’t shout out Cody from Cadence Manufacturing - his bits are excellent as well and offer a great “middle of the road” price for the quality, though his selection is smaller.
Also, Andy did a great video on bit longevity that I highly recommend.
For bit recommendations, there is a good thread here: end-mill-bits-starter-set-for-a-new-guy
Hope this helps.
-Tom