If its a small amount like 100$ better to invest in Bitvoincash or Litecoin as they are more scalable and if you are going to invest big you should have both ETH and BTC as bitcoin is the leader of Crypto and ETH is more advanced as the thienlonghue mentioned.
smart-contract platform and ERC20 will be better
No matter how small your capital is, its always better to invest in bitcoin than its clone coins because look at the growth of bitcoin cash and bitcoin, you only can see the fall of bitcoin cash since it was forked so how can you call it as investment when the value is keep depreciating.
I will still say bitcoin is better to invest than ethereum because if we analyze the growth percentage of bitcoin and ethereum in 2020 then bitcoin almost got 1000% or more while ethereum a bit lesser than bitcoin.