Too bad we can't choose more than 1, or prioritize. My list (based on a combination of factors) might look something like this:
1. Blackcoin
2. Pesetacoin
3. Darkcoin
4. Fluttercoin
I'm surprised how little I hear in terms of development and promotion for litecoin. Seems like the only advantage it has is that it was among the first clones of bitcoin. If I could short it I would. Even dogecoin or mintcoin likely has more staying power than LTC.
I dont think litecoin has much future, its difficulty has dropped significantly, although once ASICS become more common, everyone will direct their hashpower at it as a quick pump and dump. I dont see any advantage with LTC other than its faster than bitcoin and was ASIC proof at the time.
There are many coins all with good features, i feel that we will see probably POS coins being the most successful in the long term, but here is my list of coins that i feel will have major success:
1: NXT
2:Blackcoin
3:Darkcoin
4:Megacoin
Fluttercoin is too new to judge its potential, as goes with stabilityshares.
I think we will see Doge being around for some time, but dont know high it will reach.