Hello E-rock,
Sorry for the long post, but here goes.
Are you just starting out? If so, you may want to go with a short term or no contract while you learn. Once you prove yourself to the customer, you will be in a better position to lock them in for extended period of time. This also works in your favor. As you gain experience and figure out the money you need to be profitable, you are not under any long term commitment honoring a "bad" contract. Things come up that you just don't think about when you first start.
You may also find that you don't enjoy your chosen segment of powerwashing (for example, fleet washing) If you are under contract, i would think you would have to suffer, doing work that you don't like, until the contract lapses. Short term lets you learn every aspect of what you are doing and decide if this is where you want to focus your business.
We have a couple of fleet accounts that we have done for 3 years without a contract. We have not dropped the ball and given them a reason to look at anyone else, so they continue to use us.
I hope you get more input from those here who use contracts. Might help to post a little more info in your profile. People start to open up when they know where your from, how long in business, and stuff like that.
Shawn