Myetherwallet
Your right mate, just make sure all the altcoins that you want keep and hold in a long term are also listed in MEW, then always keep your private key and password to make it safe very well.
There is nothing like an altcoin being listed in MEW. If it is an ERC20 token, then that is when you can have it in your MyEtherWallet. I am surprised most people here have no idea that Altcoins in general is not all about tokens and obviously most of you have no idea of what you are even saying or you probably did not even bother to read the OP. LTC was mentioned and you are recommending MEW!
If the OP is willing to make use of an exchange to keep most of his alts, then I will say he should make use of Bittrex but I would not keep all my assets here. So it is best you make use of Coinomi, Jax or Exodus wallet.