I will recemend you to buy only coins with good name in market and avoid shit coins, TRX, XRP, NEO, ETH, LTC, XMR are some projects with Trusted team and comunity in backup. Hope you will consider my advice.
Usually we suggest to invest in popular coins because of their history and proven to be profitable for long term hold and thats what I prefer as well.
In buying altcoins I think you're the only one who can decide for yourself because it depends on the capital and the price of your chosen coins. We know the best time to buy is when the value of alts are declining, so if you have the budget to buy then do it. Just make sure you already conduct your reseach to avoid regrets later on.
to be able to determine an appropriate altcoin for investment is very difficult to do because all altcoin is not able to provide a guaranteed profit, to be able to get a profit on altcoin can be seen from the development of the platform or from your luck, altcoin will always have a very high risk so you must remain vigilant because this concerns the capital money you have.