Have been looking for the most viable altcoin of the the week, as we are all aware of the deep that is currently happening in the entire cryptocurrency market, Bitcoin is my most preferred choice at the moment but am also looking for Alt that I can invest in for a long term basis that will offer me a passive profits in the long run.
I guess you don't have to look for solid coins if you are looking for a long term investments, it's already there, the top 10 coins in coinmarketcap.
Not sure though how long are you going to hold or how much you are willing to invest.
But to give you a perspective, way back 2018 ETH for example was in the 2 digits price, meaning it's less than 100$. Moving forward it's now on the $4k price. So in a span of 3 years it has grown tremendously. So I think that will be the minimum hold, at least 4 years as per my experience.