On the off chance that you sell Bitcoin for fiat now, you will lose. It will be smarter to discover a trade with the best rates and sell BTC there to get altcoins. I would pick Gladius, IOTA, OmiseGO, Qtum, and Komodo
I would sell some altcoins only as sooner or later, they will vanish. I am sure that Dash and Monero will survive. Ethereum might stay the second cryptocurrency in the rating for years. Bitcoin has more chances to go up than go down. Therefore there is no need to sell it to get fiat. Some BTC (or Satoshi, it depends on the amount you have) can be exchanged for the best altcoins.