It depends on when you are investing and what's your plan whether you want to plan for the short term, long term, or want to trade daily so according to this you have to select the currency. For the long term, you can rely on top coins, and in short term, you can trade new coins also but for daily trading, you have to research the coin that moves daily up and down with good trading volume so that you can sell anytime whenever you want. If you are a long-term investor I believe you can invest at any time whenever you have funds for investing.