I think you should diversify your investment and buy both of them as both of these coins are phenomenal in their own sense. Bitcoin is considered master of all crypto available in the market and without any doubt is the most popular crypto in the world. You can easily expect it's price to hit 20,000$ within 2-3 years for sure.
Ethereum on the other hand, is considered master of all smart contracts and is currently the most used protocol for new projects and ICOs. You can easily expect it's price to be around 3000$ within 2-3 years