if I were you and had 0.2 BTC funds, of course I would not buy just one coin, of course I would buy several top 10 coins based on Coinmarketcap, if you have that much funds and only choose one coin it will be very heavy and big the risk you will take.
Choosing an altcoin to invest in just by its position in coinmarketcap is completely wrong. For example lets take dogecoin. Everyone knows it, it has a large community. Just half a year ago, dogecoin was among top10. Now its price is 5 times lower than it was and it is on 12 place. I remember Waves was if not among top10, but in top20 definitely. Now it is about to be kicked out of first 100.
And there is an opposite situation. Something from bottom of coinmarketcap list can release something innovative or suddenly become demanding, and quickly take top places. Dont forget pumps, they easily change altcoin positions in top. You won't even be able to blink an eye when such tactics will start to bring losses.