Only 2 exchanges are the best for me, first poloniex and bittrex though there's another contender which is shapeshift.io
Don't use yobit.net as it will just going to give you some headache in terms of their support.
They are the worst exchange after all.
Poloniex and Kraken has some issues regarding their services right now, not sure if already resolved.
And bittrex seems lead the way in term of global trading volume as listed here; https://coinmarketcap.com/exchanges/volume/24-hour/ after Bithumb, but bittrex withdrawal fees is pretty high as much BTC0.001 when the last time I've withdraw my bitcoin.
I don't know about shapesift.io, but as long as these trading exchanges could process deposit and people easily to withdraw what belongs to them, then it's your choice to trade on which exchange.
First learn how to do trading later you can go for live trading. To trade, i also suggest you to do in Bittrex the rates are bit high, but they are legit and fast confirmation to compare other exchange sites. I am very comfortable on this site if you want you can try in Poloniex. After Bittrex I will suggest this site.