This is a question that I have a ton of experience with.  I had an Agent that for some reason I couldn't match up with.  I always seemed to get a strange over/under.  After a while I gave up on my Agent and got a Shift.  I bowled my high series this year (783) with the Shift within a couple of weeks of owning it after I sanded it to 2000.  The Shift has been my go-to ball since then.

After a while I got curious and I sanded my Agent to 2000 as well.  I should have done that a while ago, because ever since I have been money with the Agent as well.

I know you didn't ask me all that - but I thought I'd give you some background so that you can get a sense of the fact that I have worked with both of these balls extensively.

When both balls were OOTB polished the Shift was a stronger ball overall, but it was a bit later as well.  At 2000 they cover almost exactly the same amount of oil but they have very different reactions.  I'd say the Shift is smoother overall - but the Agent has a stronger move when it hits the dry.  Both are what I would call 'strong arcs'.

I use the Shift when there is a clear wet/dry line so that I have a smoother reaction, but I use the Agent on more of a blended transition.

I hope that helps.