I've been with scrypt.cc since end of February and getting happier every day. IF they disappear I would be HUGELY disappointed, but that seems less likely the longer I'm with them and see their efforts in getting things better and better. Keeping a website safe and accessible during weeks of DDOS/hack attacks and investing quite a bit of money in even better anti-DDOS measures doesn't sound very Ponzi to me.
Okay, one of the benefits scrypt.cc has over most others mentioned (I don't know all of those, but I have a rig pointed at Wafflepool at home) is the fact that they have all of their rigs hooked up inside professional data centers, using professional quality networks all over, including high grade connections to the internet, and everything is monitored and serviced by professional personnel. While that might make just a few percent difference, you'll have to multiply that tiny difference by a few thousand rigs. The average home user is not going to get such blazing fast quality connections.
Also they've setup (or are still setting up) all of their rigs to mine scrypt, scrypt-n and scrypt-jane coins, which means they have more coins to chose from, with less competition from asics.
One other thing, though I'm not sure about that, is that they mine three coins at the same time
Last thing is of course that they use their own scripts and rules to calculate the most profitable coins. Different approaches have different effect. Unfortunately they're not willing to disclose how they do it exactly. Can't blame them. Why flag others for good coins to mine if that means the difficulty will spike even more, making that coin less profitable
suchmoon, I love this spreadsheet of yours