If I have access to currency-specific variables/datasets for any cryptocurrency of choice (see below), how would I calculate which cryptocurrency (out of a fixed set of say 3-5 altcoins -- SHA-256 and Scrypt only) would be most profitable to mine at a given time?
Given: difficulty, hash rate (network), block count, block time, block reward, exchange rate, and exchange volume.
To be more specific, I'm wondering what math would go into calculating Expected Earnings/(MH/sec) for each cryptocurrency with this data? I'm not not necessarily asking for something like http://www.coinwarz.com/cryptocurrency/ that takes your own device's hash rate and power consumption:power cost ratio to determine individual profitability, I'm talking about a general calculation where the output is in the units 'Expected Earnings/(MH/sec)'
(I'm not sure how complicated a calculation like this is, so I'm not asking for exact math or anything just where/how to start with a problem like this)