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.
That's probably a good idea not to buy coins like that for the reason you gave.
I own some altcoins, not many, and my interest is exclusively in proof of stake coins. I have a hard time owning anything that doesn't pay at least some income on an investment, which is a mindset I acquired from years in the stock market. Bitcoin is an exception to that, but altcoins aren't. Therefore I wouldn't own any coins you can't earn rewards on. Navcoin, NEO, and a few others I love because of the ability to earn.
Aside from POS coins I wouldn't think of owning any altcoins that were ranked probably 50 or lower on coinmarketcap. Anything below that would seem to be purely speculative and ultimately unprofitable.
Good thread, op. Not many people talk about what they don't want to own.