I think cdj24 makes a really good point to think about the company. When thinking of how to answer, I was leaning more towards the idea of having a negative CV and a positive SV, as I think it would be better to be slightly over budget, yet ahead of schedule. Not that you would want to cut back on future costs, but it at least gives you the option, right? Plus being a ahead of schedule lets you focus more on the project. I think that if you’re behind schedule, you might make jumps or look for shortcuts.
However, considering cdj24’s comment, if the business is focused on saving money, or rather a start up with little funds from the get go, then having a negative CV would not be a good idea (though I am disregarding the behind schedule part).
I think it would be best to keep them both positive so if one becomes negative then you should stop back and take a minute how to fix it as appropriately as possible.