This is the 1 million question! I can't imagine a person who can say that for sure. But, if you wanna a guess, here is mine: buy anyone between top 10 and you'll be fine. Just hold, take your time and you'll get profit.
This might be a good advice but it also might be a bad one... Can anyone guarantee all the top 10 will keep on growing? I strongly doubt that!
I believe some of the current top 10 are super hyped and might collapse at any instant. On the top 10 I would only bet on BTC, ETH and LTC.
A better advice might be to buy a good top 200 coin, with a solid reputation and a clear future strategy. There are a few on fit in this description but my money is on Diamond Coin. Just check it out.