Without being able to review your entire history it will not be possible to give you an exact answer, however both options have its pros and cons which you should discuss with your cardiologist.
Neither amiodarone nor LifeVest help with heart failure symptoms as biventricular pacemaker/defibrillator does. However they are used to protect from lethal arrhythmias. Life Vest would likely be more effective for treatment of these lethal rhythms but you mentioned that there is no history of defibrillator shocks (i.e no history of lethal rhythms or no history of lethal rhythms long enough to warrant therapy). Amiodarone have frequent side effects, most (but not all) are associated with long term use. Obviously it is not a case with using LifeVest.
On the other hand you mentioned that biventricular pacemaker helps for ‘irregular beats’. If that’s the case amiodarone could be a better choice as it may suppress some of the irregular beats (including most frequent complex arrhythmia i.e atrial fibrillation).
Insurance coverage and cost of LifeVest should be also considered.
I would strongly encourage you to discuss all of these with your cardiologist prior to making final decision.
With best wishes
I'm not a physician and haven't had any experience with amiodarone, but I did recently wear a LifeVest for 3 months. I have a CRT-D now. Personally, I would want both unless there is some contraindication to using them together. The LifeVest gave me a great deal of security and I was very grateful to have it while we gave medication a trial. The LifeVest cost $3200 a month.