It could be both, depends on your specifications on how you put your venture with but definitely I would go to BTC hence this is the buy zone of bitcoin right now due to bad market sentiments. Some altcoins are worth it too, any top 10 on CMC is nice to buy and hold too.
Yes bitcoin is the best among bitcoin and altcoins the demand for bitcoin in the market is huge and the value of altcoins increases depending on the price of this currency. Despite the bad situation in the market, the demand for bitcoin is high if the price goes down if you wait patiently it will rise to the top.