bitcoin is always going to be the best thing you can hope for in a long term investment and altcoin can be the best for short term investment. other than that altcoins are not good for long term because they don't have the adoption like bitcoin has which means their rises are pure pump based on speculation and fear of missing out. these rises can not last on their own.

besides you are in trading discussion board so it is about trading and making profit from that. in trading altcoins you only buy those that are about to go up. if you look at the history of altcoins you can see that period only lasts a very short amount of time. hence good short term investments.
in comparison bitcoin rises in short term, has some correction then starts rising again short after. hence good long term and short term investment.