I've been mining LiteCoin (LTC) for a while now, and I have noticed that amongst the various Scrypt coins listed on coinwarz.com, there seems to not be a direct correlation between the coins' difficulty, hash rate, and how many coins you can expect per day.
There is, if you take into account the block rate and -reward.
100 coins every minute vs. 1 coin every 10 minutes will yield a difference of 1,000 : 1 using the same difficulty.