I would say only BitCoin could be interesting to hold. Short term thinking, several Crypt coins could be used for exchanges or speculation, but in the future, only one bitcoin can predominate, maybe can be competitors, but I donīt think that you can get much profit of them.
There can be more than one big coin in the future. I don't think there will be as many as there are currently out there today, but BTC and LTC should be major players for a long time.
It's worked before in other commodities. Gold and silver, for instance, are in the same category of investments, have been around a long time, and people buy both.