Right now, bitcoin seems to be booming and cashing out from it for an alt could be a hit or miss, while bitcoin could keep rising in price. I'd say that there's no such thing as "best coin", but really it's all just talk. People say that ICOs is where it's at, but while some seek quick profit there, this is also something seeming like a bubble and not too sustainable.
I agree. Bitcoin is still the king of all cryptocurrencies, therefore, it is still the best medium to trade and invest on. However, since it gained so much price and value during its previous price surge, any investor would have to shed out a bigger capital than before, but in terms of the viability of the investment, I would say that bitcoin would still be the safest to rely on. On the other hand, there are still some promising altcoins out there that could be considered like Eth, Waves, LTC, Ripples, and Dash. It's just up your liking where you would invest your money.