Feathercoin, Megacoin, and Quarkcoin are all in the top 10 by market cap and worth of inclusion.
Of those, priority should be given to Feathercoin as it has the most active community and well developed user base, plus much higher trading volume than the other two.
I'm afraid we have agreed to have a blanket ban on Feathercoin. Our advisory board does not believe it has a future. It is clearly a commercially-backed coin, not a product of the open source community. The strength of the order books are definitely artificial - they are too regular and too big. Also, there are many shills out there from what I can tell. Just hang out in the BTC-E Trollbox for a bit!
Megacoin is one I'd like to understand more. It has outperformed all other coins in terms of value this week (a 200x increase). But why? What is special about it?
I had not looked at Quark before. I thought it was just another scum coin. That looks very interesting indeed. A coin with a USP focused on security is definitely a niche. Of course there's the likes of Cryptogenic Bullion which strive to be extra-secure, but I don't think they have actually made any differences to the base scrypt coin other than increase the confirmations requirements.
Kate.