I have experience with both of these meds.

Xanax is a great drug - fast acting with few side effects. Fatigue is the only real side effect I've ever noticed with it.

Lexapro is the AD I'm on for my anxiety and OCD. For the first few weeks, it made me nauseous and decreased my appetite, but that went away. It also made me a bit fatigued, but that too went away. I find that it's extremely effective. It's my favorite out of all the ADs I've tried. I felt a difference within about 2-3 weeks of starting it which is fast.