The best crypto which you can think of holding is Bitcoin. Holding Bitcoin feels like holding something reliable. But is it as far my opinion and views.
As you have said that you wanted to know that which Altcoins should we hold in order to get profit, so let me make you clear that it completely depends upon yourself.
Let me give you an example, suppose you want to gain a huge amount of profit in a shorter period of time, then invest in the coins whose prices are more volatile. This may led to self-destruction too, as the prices will be highly fluctuating. So you may occur loss.
But let's say, if you want to gain slow profit, then just invest your money in more stable Altcoins. There is less risk in this type of investment.

Atleast according to me, the best Altcoins to invest will be Eth, LTC, and Ripple.
Hope this helps you.