i think you start Altcoin trading from yobit and a huge of people are also using yobit for trading because yobit is much more good and secure and yobit is very popular and i also using yobit for trading .
for me yobit only be good place to train your skills in the beginning .
but not good at all later if you continue trading for long term.
they are indeed have a lot of choice to trade altcoin.
but yobit for me morelikely to a scam trading platform if you trade in high amount.
I mainly use the Poloniex for most of my trading. If the coin is not liquid, I will use the Bittrex. It is also good.
poloniex and bittrex are the most trusted trading exchange that have a lot of altcoin listed
i will believe on them for now , but never believe 100% of course
just avoid to trading on yobit ,this is personal advice (ignore me if you have different thoughts)
trading altcoin also frequently feel like gambling , as the price looks bouncing randomly