Which slogan sounds better?

Get rid of options 2 & 4. ‘Make it Count’ sounds like an accountant. I like the first one the most out of those 4. Maybe something like, “Solving Impossibilities” would be better.

Make it count is the only one I have never heard before. It still has a generic ring to it though. Sorry if that’s brutal but I’m just being honest.

I don’t like any of them.

Can so!

Definitely not #3 or #4. #3 sounds like a cheerleaders’ chant before an extra point. #4 sounds cheesy. #2 is alright, but it does sound a little generic. A variation of #1 might be nice.

Outside the box or
What Box?
Beyond the Possible

Possible impossibilities?

The Impossible and Beyond

None of them says “creativity is our forte” to me. Are you selling creativity or tenacity?

Perhaps take a cue from the Strengthsfinder categories and use that to make a correlation:
XYZ Agency: Execution. Influence. Strategy. Relationships.

You could then use the strengths associated with those categories as talking points for how the agency is able to accomplish the impossible by whichever of the strengths best fit your agency’s work model. The ones that I would find attractive as a potential client would be: achiever, arranger, consistency, deliberative, focus, activator, communication, maximizer, adaptability, connectedness, relator, analytical, context, ideation, strategic.

Since you asked, I don’t like any of your suggestions. I think that the company’s mission statement should be condensed into one short sentence. If that can’t be done, drop the slogan and send out a cut-sheet describing the company’s products and services to potential customers. I know, from my industrial experience that those cute slogans do nothing to influence me. I deal with companies that produce without all the fluff.