You're going to find a 1000 answers to that. My way is to look at people first. Who are the users of a particular coin. Then I look at the landscape, what are the users using it for? and then I look at the future, where can this become useful.

bitcoin for example, the predominate users are investors. the landscape is becoming banks and wall st. what they are using it for is a store of value. for that reason alone, I dont think btc is going anywhere anytime soon, but by that same account, it isnt going to be used for day to day transactions. you'll need something like LTC to accomplish that.