CPU is undoubtedly better for mining any type of cryptocurrency than high amounts of memory.
However, with Protoshares at least, it is best practice to choose an amount of memory that is a multiplication of how many cores you have, due to how the miners we use work. For example, if you have two cores you should have a minimum of 1.5GB of memory due to the least recommended memory amount per core being 512mb (512mb for each core) with 512mb free for the operating system. If you have 4 cores, 2.5GB ((4x512mb) + 512mb for OS), 8 cores 4.5GB and so on.