Humor, sarcasm, cynicism and eloquence are usually not good components of an effective mission statement. Simplicity, honesty and frankness are. Avoid saying how great you are, what great quality and what great service you provide. Using these concepts makes you indistinguishable from the rest. Effective mission statements need not set the world on fire.
Lofty statements have little credibility.
The best ones are direct and powerful. Make certain your statement is you and not some other company. That is why you should not copy a statement. Even if your statement is a little unpolished it will appear to have more credibility and integrity than if it portrays you as something you are not. Make certain you believe in your statement.