Investing in top coins are the safest way in my opium.
Ethereum has proven to be a solid coin and therefor a good choice for long term investing.
Indeed, eth is one of the best alts to invest nowadays.
If you are not a fan of diversifying then choose eth and bitcoin. These coins are well-established and has many supporters thus even the market turns bearish for sure these coins can bounce back and can reach another ath though it wont happen in snap. Thats why we need patience because we dont know when it will going to happen.