Almost alt coins and bitcoin are going on the down trend in recent days. I think putting all in 1 coin or several ones is not different. The only thing we should aware of staying away any scam coins.
In any movement of the market up or down, you should always have a portfolio consisting of several assets, regardless of the current market. This is a mandatory rule of the investor. I also think experienced people have no problem to distinguish a promising project from a scam project
Several assets you mean from the crypto area or in general? As you can see even if you diversify in the crypto sphere it's all going down at the same time unless you have a good portion of a stable currency to hedge.