I would definetly suggest you to invest in bitcoin as it is the most trusted investment in the crypto world. No one would help you choosing another one better than bitcoin. But if you really looking for one, better to make your own researches and learn about investment principles which depends on your willing of investments (long-term,medium-term,long-term). Good luck
Yes BTC is a good one for long term investment also focus on altcoins as well, you see ripple is trending from few days ETH has a good move in crypto Market. These coins will rule the crypocurrency in future. Yes need to have knowledge in this field. You need to react according to the market situation if you need a good return.
I strongly suggest for investment against the Ethereum. because with the ability to develop owned Ethereum is able to generate more profits by investing even more coins. I also like its development were present as well as continue to support it, thus I gave to you.