For me the best choice would be Bitcoin because it has the biggest community, enthusiasts, adopters, merchants and countries accepting as payment system. Bitcoin has been tested and proven by many as safe investment and payment method and also Bitcoin had passed all those harsh or devastating crashes and attacks from the volatile market which Altcoins needs to handle or take risk of in the future or else bleed to death. Altcoins are dependent to Bitcoins that is what I have observed on the market even though whales or something like that are manipulating some Altcoins to skyrocket but will still depend on Bitcoin in the long run. Though Altcoins are more profitable these days than Bitcoin because of BTC's price too high nowadays but Bitcoin will still be the best choice for long term investment.