They are both great commuter bikes. Which one for you? Depends on your terrain and riding style. If it's mostly flat with distances under 30 miles the Vado 3 should do it. With hills and/or longer distances the Vado 4 is the one. Test ride both if you can. You'll get an appreciation for the motor torque and power differences.
My wife and I ride Vado 5s in a very hilly little town. Yes, they did cost more but more than a year later we've never said "gee I wish we'd saved some $ and gotten the bikes with smaller batteries". I often get home with 15% or less battery left on our 600Wh batteries and now do rides where I need to take my wife's battery with me to finish the rides.