What has a lower long term cost per hash: LTC, BTC or other alt coin? I'm trying to understand the cost per hash operation with Litecoin vs Bitcoin over time.  The theory is that the network that has the best prospects for long-term security (via hashing) will set a standard that may influence its own price.

Specifically I'd like to compare


Capital outlays (reasonable mining hardware ASIC vs GPU)
OPEX (Electrical, etc)


Suppose I were to compare BTC/Litecoin mining to ore mining.  Once the ore is extracted and purified, no more cost is needed other than to secure the facility where the gold is stored.

Its clear the mining process is technology dependent (ASIC vs GPU).  What isn't clear to me is once the technology matures, what approach has a greater chance for long term efficiency for maintaining and securing the network.

I suspect that the scrypt -vs- sha256 implementations will have different power requirements, and I'd like to understand which one is "greener" for the environment in the long haul.

Any information relating to


Cost of current mining rigs to power efficiency
Cost of future mining rigs and projected efficiency 


Would be very interesting.
One of scrypt design goals was to make CPU and GPU performance balanced, which meant that it was far more dependent on memory speed. 

The GPU had a solid work around and as far as I know CPUs don't have any advantage.

But that did cause it basically impossible to do scrypt mining with an ASIC unless it has a ton of memory and memory channels added in, which is a huge design problem.  Unlikely unless GPU mining for scrypt is very profitable.

This also makes Scrypt far more energy intensive for the same amount of useful hashing, but the network adapts as it requires far less hashes to solve problems (Difficulty number)

Which is greener? By far ASIC mining, it's power usage is tiny compared to performance, 4500MH for 4.5w vs 275MH for 100w.

But again, the network balances.