For current market the best ones are BTC and ETH without a doubt! Going for alts may be not very wise for current situation, market is still very volatile.
First check the coinmarketcap observe the top 10 to 20 then have some research for the coins which you think is really good in your sight anyway. Then once you prove that it is potentials and deserving to buy, do it only on buying what you can afford to loose. Like for example Ethreum, Qtum, Waves, Xem, and Neo.
Actually now we can invest in any coins because all altcoins and Bitcoin prices are down and stable from last few weeks. I think people those who have enough investment they can go with BTC, ETH, NEO if you have low investment then you can buy IOST, NEM etc.
Yes, the above-mentioned coins have very huge potential in the market because we have seen their previous growths in the market and definitely there is a huge chance for them to grow their value in the market.