Long term investment in altcoin projects seems odd to me. They are easily manipulated, which means those who are in for short term investment and trading can make profits if the project is monitored frequently. However, I believe long term investment can still be possible if the investor isn't seeking quick profits. Some people simply buy coins and hold onto them until they choose to remember or engage with them.
To me, long term means 4 years or more, not a few months. In this case, we need to find ALTS that have new ATHs in each new cycle. ETH, LINK, BNB, ADA can do it, while LTC, NEO, EOS, TRX and many other ALTS cannot. At the same time, we already have BTC as the safest crypto asset of all ALTS, BTC also has new ATHs in each new cycle. So, if holding for the long term, BTC is always my favorite choice and BTC usually accounts for more than 50% of my portfolio.
ALTS are also really attractive and they can be considered in a bullrun, when we enter altseason and ALTS outperform BTC and generate greater returns for investors.