Let's take at what I know about Zipcar (ZIP.DL2). First, the company provides a car-sharing service that my wife and I find extremely helpful, as we use the car parked down the street from us in Chicago at least once per week for various activities. Second, the company's stock is up almost 20% since it released earnings last week. And finally, I plan on giving it the boot from The World's Greatest Growth Portfolio.  

The juxtaposition of those facts might seem odd, but there is a method to my madness.

A few weeks ago, I outlined exactly how I would go about building my portfolio for next year: Invest first and foremost in companies that demonstrate exceptional levels of innovation, with special emphasis given to those that I believe will be around decades from now.

Despite all the good news coming from Zipcar recently, I just don't think it deserves a spot in my portfolio -- which has significantly outperformed the market -- in 2013. Read below to find out why, and at the end I'll offer up access to a special free report detailing what I consider to be far better choices for your portfolio.

Don't get me wrong, I love the service
As my wife and I have grown older, we've tried to own less and less "stuff," and Zipcar has helped us immensely in that regard. Moving from spot to spot mostly on our bikes has been great for our health, and for connecting with our local community. But when we do want to use a car, we're very appreciative for Zipcar.

And the most recent earnings release was definitely a cause for celebration among shareholders. Revenue rose a solid 15% from the same time last year, and more important, new-member sign-ups rose 18%. On top of that, earnings per share quintupled, from $0.02 last year to $0.10 today.

With the company opening up services in more and more American and European locations, and a favorable  partnership in place with Ford (F -1.26%) it's easy to see why some are excited.

So what's the problem?
Unfortunately, I'm starting to think that it's the car-sharing movement, and not Zipcar per se, that is truly innovative. I love not owning a car, but there have been many occasions where I needed a car to travel somewhere, stay there for a while, and then bring the car back.

Unfortunately, since Zipcar is not a point-to-point service, I'm getting charged the whole time I'm at my activity and my car is simply sitting there. Daimler's car2go program, which offers up the use of SmartCars that are located throughout several U.S. cities, is different.

Instead of having assigned spots to leave a car in, users can simply park the SmartCars on any city street within designated areas. Of course, there's no guarantee that when I need to return home, the car will be there. At the same time, the much lower-cost and lower-stress model of car2go seems far more appealing to me than just having a Zipcar sitting there while someone else could be using it.

And car2go isn't the only competition. Hertz (HTZG.Q) has its Hertz On Demand, and is completing its $2.3 billion deal for Dollar Thrifty (NYSE: DTG). There's no telling how the combined companies plan to move into the car-sharing space, but you can be sure that it gives Hertz more options.

And so, I chalk this up to a lesson learned: Zipcar is innovative, but it's the trend of car-sharing that's truly a difference-maker. Just because Zipcar was a first-mover doesn't mean that innovation is in the company's DNA. If it was, I truly believe it would have begun offering point-to-point service years ago.