I hope you know that one of the basic concepts of litecoin was to try and prevent GPU domination of the mining activity. Your gpu will not perform the same as it does on BTC.
And do you know that despite that litecoin runs VERY WELL on ATI GPU? Much much much faster than on CPU
As for btc vs ltc, everything depend from the price and the difficulty of them. But cpu mining litecoin? Fail.