To be sincere, since you don't know the type of coin to invest in, then I would suggest you start with top coins, depending on your funds, top 20 in coinmarketcap is a good way to start. Also, to be sincere once more, no matter the coins you later decided to invest in, let Bitcoin be in your portfolio, it is the best to hold or invest in all the time.
Lastly, one of the things to consider first before investing in any coin is the team and their level of commitment which reflects on the platform's growth.