It is true to say that ETH is the best alt coin. Coins are as valuable as their endurance in the market. As is obvious, so far BTC and ETH are the ones which have proved their logetivity. In terms of other alt coins I would suggest buying for long term profits( short ones are risky - the pump and dump game will trick you at some point, no matter how good you are at speculating). I would look at the projects they are representing, their prospects on the market etc. For allt coin which is dipping at themoment I would look into AMB.