Litecoin. That's probably your safest bet.
Litecoin, Peercoin, Namecoin are all old, high market cap, and trusted. When MT Gox adds alt coins, they will be among the first. 2014 may be the year where we see big exchanges that once only traded BTC finally added new ones.
Trusted by who? Everyone seems to have a different idea about it. The BTC zealots only trust BTC everything else is a scam. Then next wave of adopters only like PPC LTC NMC everything else is a scam. The next wave love everything they own and the coins they don't are a scam.
Do your own research, people on here will just tell you what their portfolio wants them to say.
Coins with great opportunity... LTC, MEC, DIGI, QRK, CGB WDC, - - For me Digi is very undervalued even now. Right now QRK is the big talk that coin is not going away anytime soon. MEC large following. LTC - well come on everyone needs to hold a bit of LTC. PPC is split a lot hate and lot love. I would hold a little of that too. NMC seems a cool idea, so again hold a bit.
Outright gambles but good chances. TIX ADT NET and some others , gambles can pay off but more risk.