Try to select only those altcoins which will have reliable and known developers and will have a good number of investment and will have a good volume of trade.
Yeah these features are most affecting the value of any altcoin, coins with that features will have good potential to increase in value in the future so any person who will have investment in that coin will not be disappointed and will earn a good profit in the future when the value will increase.
You do not know beforehand how much money people will invest into the altcoin, do you? Transparency truly is an important feature to determine a coin's reliability, but even when everything seem cool, there is risk so you are still advised to be cautious and keep your eyes on the development progress and check that it actually is progress, not simple forking.