A good lawyer can get easily get you aquitted of DUI if you refuse both the BAC test and sobriety test.
Giving a breath, blood or urine sample and submitting to a Field Sobriety Test is giving the court all the evidence it needs to convict you.
Without that evidence, there is "reasonable doubt"
Unless you are on video, falling down drunk, or the DA produces other evidence like credit card reciepts of all the drinks you bought that night at a bar, plus numerous witness, which is unlikely in a DUI case unless there is an injury and/or death involved, a good attorney will easily get you aquitted.
You will lose your licence for a period of time, depending on which state you live in, for refusal, but it's better than being convicted of DUI.
Either way, it's going to cost you a lot of money.
Don't drink and drive and you won't have a problem.
It's similiar to getting pulled over for speeding, and the officer asks "Do you know how fast you were going?"
He's trying to get an admission of guilt to use against you.