I would think a One, not a Big One, would be a better comparison for an Agent.
Take this with a grain of salt, because I've thrown neither, personally.
As for the One series, I've noticed for the original One, it matches up either extremely well to a person's game or it doesn't match up at all. People who like that ball tend to be dominant with it. People who struggle with it REALLY struggle with it.
I forget what grit the One comes, but it's polished. The Big One comes 4000 Abralon but it feels rougher than my Lanemasters Yeah Baby, which I had adjusted to 4000 Abralon about a month back. The Big One looks too aggressive, in my opinion, for most house shots. However, I see it used fairly effectively where I live. And there seems to be less of a "love it, hate it" phenomenon with that ball than there is with the original One.
I've got a pretty good idea of what an Agent would be like, given that I've thrown about 15-20 different Storm models over the years. If it behaves like I think it will, it will be more angular than the Big One but not uncontrolable. As mentioned above, another option for you is the Storm Pyro, which as a particle pearl would give you even greater controlability.
Someone above mentioned an Elements Ice as a comparison ball for the Agent; I have an Elements Ice and I love it. But I don't think it's necessarily a comparable ball to the Agent. I would expect the Agent to flare more and to be far more angular.
Jess