I'm used Bittrex, I find a lot in Bittrex profits, exchanges are also easy and convenient, but Polo better because a large volume of transactions. The transaction fees at Polo and Bittrex equivalent.
# 3 has not thought out the optimal way
I will go with your statement. Bittrex have more influence than other exchanges in terms of usage. The convenience, high profile safe and security Bittrex providing cant be seen in any other exchange. Although we have not that high volume of transaction at a time but still is be better.