Bitcoin would be best for 5-10 year investment. I cant even imagine how great botcoin will be in that span of time. For other coins, you can also go with ETH, LTC, OMG and NEO. Im holding these coin and planning to do it for long term as well. I believe that these coins will have a good future, they are developing, innovating and they good for long term due to their stability, so I for me, these coins are safe.