At the Texas Cardiac Arrhythmia Institute in Austin, Dr. Andrea Natale. You can call, ask for a consultation, and chances are good that you'll be selected, particularly complex cases and repeat ablations that have failed shortly after the patient is discharged by the performing EP. Dr. Natale sees patients in several hospitals in the American west where he has privileges, so he travels now and then to do ablations elsewhere besides just Austin.
The only other one I know of who is highly regarded is Dr. Pasquale Santangeli at Cleveland Clinic. Note that there are at least 20 top notch EPs scattered around the USA, but as a Canadian, I only read of them now and then when reading forum posts and don't remark on their names, so I can't pass them on.