Yea the volatility of the altcoin maybe is the key factor for trading but there are still 3 important questions we can ask for the trade.
1- Which altcoins do you prefer for your daily or short time trade generally?
2- And why do you prefer?
3- Do you have any daily income goal or you trade as much as you can with this altcoins?
for day trading you need a big altcoin which has a large daily trading volume that you can use in your advantage and make profit from short term dips and rises. so in short coins with large volume, doesn't matter what they are.
how ever for short term trading. i consider it to be a bit longer than just a couple of hours in one day. if we are talking about longer (a week for example) then many coins that are on the verge of a pump are good. and they are different each week.