A lot of discussions on forum are all about "what coin should I buy? Why?"
Here's the opposite - I want to ask what alts you would never buy and why so.
My example:
Never buy BTT, Tron, Stellar and other coins where the tokens are giving away with all kinds of airdrops. Why? Emission grows with no influx of investors.
Doubting about Peercoin. Hybrid emission system doesn't seem reliable too, though lately PPC began spreading itself via well-known exchanges (changheangel or changelly - don't remember).
+ Libra. Not sure if any explanation needed.
I have my own ideology about the altcoins I should invest and they are the ones I have seen that are really working while looking for more ways to expand, and as such Stellar fits this description. Am not much of a fan of Tron but I think the team is active in their own ways far more than most projects. The type of altcoins I stay away from are those being hyped by so called experts, or those whose team have proved to be inexperienced in what they want to achieve. Also, even if a project is listed, I always tend to check to see if the project is really in line with their roadmap etc.