Computer Science vs Computer Graphics Masters
I'd look at this a little like a wager on where you want to go in the future. 

If you'd like to do a PhD in the future, then focus on the fundamentals will pay off. I can't think of a single PhD that wouldn't benefit from stronger research and math skills. Especially if you want to go on to a PhD, ensure that you're getting the background in research --- typically this will mean a focus on thesis based programs. 

If you're unsure of where you want to go afterwards, be aware, that a good master's program in Computer Science, is unlikely to close any doors for you, whereas a focus on Computer Graphics may mean that it's more difficult to make the transition into a different field later should you decide it's not for you.