I've heard a lot of myths out there masquerading as legal advice regarding whether or not to blow. If you've spent enough time at the pub, I'm sure you've heard them too. I once heard someone say, "As soon as you get pulled over, step out of the car and chug a flask of whiskey. That way, they won't be able to prove you were drunk while driving." This is obviously bad advice and I don't recommend that anyone try it.
The fact of the matter is, whether you're aware or not, you already consented to this chemical test of your breath or blood before you even got pulled over. Missouri's implied consent law says that you agreed to it when you chose to drive on our public roadways. By refusing to submit to the breathalyzer, you're actually making your license situation worse.* For first time offenders, you're turning what would otherwise be a short license suspension into a full-blown revocation which lasts a year.
As boring as this will sound, my advice to you is simple. Be friendly with the cops, do what they ask, and call your lawyer once you get out of jail. Now is not the time to behave like a jackass. A DWI isn't the end of the world, especially if your lawyers know what they're doing.
*Not all driving records are the same. This advice applies best to first and second time offenses.