it depends. i personally keep a constant 10%ish in Doge. its an easy store of value. buy around 40, sell around 50. 7 times a year
as far as a long term investment, you have to ask yourself, other than a store of value, what does DOGE DO for you while you hold it?
the answer is not much.
whereas other coins could have PoS mechanisms that make you some interest while you "long term hold".
all in all if long term investment is your plan, doge may not be the coin for you. BTC might be! haha
hope that helps, it's just my opinion anywayz ;p