If you plan on buying for a long term investment,always look for coins with an actual value.
In order to differentiate the good ones from the shit coins your priority is research and learning as much as you can.
This kind of coins are usually unique and actually offer some new ideas and concepts.
Now,if your primary interest is making profit then it's a different thing.
Then look for coins which have established community,and a lot of supporters.
They are often objectively nothing new and innovative,but they create hype and then dump in price,on which you can make some bucks.