“What is the most energizing antidepressant?”

Research shows that for the treatment of "uncomplicated" depression when given to large numbers of research subjects all antidepressants are about equally as effective. That is to say, about 80% of those tested get better...however, they are not the same 80%. One antidepressant may work for person A and not person B and vice versa. The cautious and informed clinician will consider the individuals subjective complaints such as being more lethargic or more hyper, more prone to sleeping excessively or sleepless nights.... Other issues may come into play as well such as whether the person is employed and what the nature of their work is. For a presumably retired individual of age 70 or someone not working in a high energy field such as law enforcement, I find that Wellbutrin often gives patients both a positive attitude after one to two weeks, but also more energy and a boost to their real and/or perceived productivity. Prozac would be my second choice.

Wellbutrin, Prozac, Zoloft, Lexapro etc

It varies from one patient to another depending on the symptoms, but if you cannot sleep or eat, I like mirtazapine.

More appropriate would be what antidepressant's are less sedating in the elderly. Most SSRI's have a low side effect profile in the elderly.
Understanding the source of the patients depression is important (dementia, Parkinson's disease, hypothyroidism etc).