Yes, all crypto investors should keep some bitcoin in their portfolio. I usually keep more than 50% of my crypto investments in Bitcoin and rest of them I will diversify in other altcoins.

Each individual will have their own preference to invest but from a long-term perspective, NEO, IOTA, ETH, LTC, NEM, Waves, OmiseGo and QTUM  may be good options. These are some of the good projects so expect good returns over the time.