I personally use Cryptopia and I like them. I have also heard good things about C-Cex. With Nova defunct and Yobit unreliable, even downright shady, stay away. So Cryptopia and C-Cex are the best options to buy XBY.
I use Cryptopia far more often than the others. C-CEX was the first exchange to have XBY, so if you want to get a bit nostalgic, head over there. I personally have had no issues with C-CEX either.
Cryptopia is best with bigger orders but now every exchange is working fine, even Yobi is working fast and nice
Yobit is peculiar. I see a lot of bots running there pumping up obscure altcoins. Cryptopia often has higher prices but is usually where I go. C-Cex I avoid though. A coin I hold has had a lot of problems with them using shady tactics to make extra money.
I also recommend using Cryptopia. Nova is also actually a good exchange but sadly they will be closig next year.
Cost mainly. Listing on Coinexchange is 2 BTC and HitBTC is 5 BTC, I dread to think what something like Bittrex would cost.