What is the best exchange to buy Blackbytes?
Bittrex, if you are willing to do a verification first.
Otherwise I made good experience with cryptopia.co.nz as well, although the Byteball trading volume there has recently been decresed.
internetofthings5 is asking for Blackbytes. I do not think blackbytes are available on Bittrex (or the other exchanges).
You should try the slack channel or the bots to trade blackbytes.