Which is better for a tummy tuck, Lovenox or Arixtra?

Both medications are effective at reducing the risk of DVT in high risk patients in combination with mechanical prophylaxis such as compression stockings and early ambulation. Both do, however, increase the risk of post-operative bleeding complications, even life-threatening bleeding. One advantage to arixtra is that it is more effective when the first dose is given after surgery, allowing your surgeon to assess the surgical site post-operatively and make the decision to use or not use anticoagulation based on your exam, thus avoiding a major bleeding episode, but also increasing your risk of a clot.  Your enzyme deficiency and history of prior DVT do make you a high risk for DVT/PE, so you should carefully consider any elective surgeries. 

Given your history I would recommend a consultation with a hematologist prior to having your surgery to get best advise on how long and at what dose you need to take anticlotting medication.  You are certainly at increased risk and I would not operate on you with this history without hematology assistance in management.  Tummy tucks are the #1 cause of DVT in plastic surgery.