I would probably advice you to invest in all three of them as all of them are very popular and have alot of potential. They can show good amount of growth in future and you can expect healthy amounts of profits from them in the long run.
BITCOIN is the master of all cryptocurrency and is without any doubt, the most popular of all cryptocurrencies available out there. It is the most stable and most widely accepted crypto available in the market.
LITECOIN for its lightning fast transactions and almost zero transaction fees. It is almost 4 times faster than Bitcoin as it has a block time of just 2.5 minutes. You can expect it's price to be above 300$ within 2-3 years
Ethereum is the most popular platform for hosting ICOs and new projects. It has a very strong development team and you can expect it's price to be above 1000$ within 1-2 years.
A diversification between all of them can help you reduce the market risks.