I think actually XPM (Primecoin) would be the right choice as only 1 pool online for now
You can then choose BTC or LTC but market is busy for them as pool operator.
You can also select any other small alt but you would surely close your pool in next weeks when rush is passed. XPM seem right choice when looking on ypool.net having sometime 4000 miners.
Primecoin definitely in a distant third after Litecoin at this point. And the fact it has only one pool is detrimental to the health of the coin. I have 7 miners and would personally like to split them between a couple pools.
Another possibility would be Novacoin which seems to have a good deal of interest.