Most likely both of them! I say that a little tongue-and-cheek, but there is some truth to it. Figuring out which Demo Fork is right for you is a little challenging, especially if you've never used either before. After all, this isn't your grandpa's wrecking bar. This is a new animal, and we get a ton of questions as folks try to learn more about them.
If you are a contractor, we generally recommend having both sizes available in your tool trailer. The 56 inch large size will accomplish the most amount of work in the shortest amount of time. But the smaller 40 inch size works much better for tighter spaces, as well as applications that don't require the extra leverage and weight. Let's look at siding removal for example. Which one will work best? As usual, it depends. If you are working from the ground, in fairly good physical condition, and are removing wood siding that's really fastened well, the 56" is going to be the most useful. But let's say you suffered a shoulder injury that limits you to lighter tools. The 40" is still going to work very well, but probably not get the job done quite as fast.
If you are a Do-it-Yourselfer, you probably have to be a little more careful with costs. After all, if you buy every tool that helps you do the job faster, you might be better off hiring a contractor. However, buying both sizes can still make sense. If your project is big, or you foresee several other projects down the road, you will still be happy with the having both wrecking tools around. Once again, it's a question of "what's your time worth?" After all, time is money and a highly valued resource. If you're in sales and Honey Badger Demo Forks save you 1, 2, or 3 days worth of work on your project, what was your earning potential for those days? Not to mention the value of reducing frustration.
Having said all this, a safe bet is to start with the smaller 40" size to get familiar with its capabilities. You can always order the 56" size later on if you find yourself needing more leverage and weight to get the job done.
Remember: Honey Badger Demo Forks come with a 30-DAY SATISFACTION GUARANTEE. Simply return the tool(s) to us for a full refund if you are unsatisfied with the purchase for any reason.