The electra, in general, is better. But a cheaper steel frame beach cruiser still makes a great electric bike.
frame weight does not matter so much if you are going to put a 15 pound hub motor from amazon on it. Then use a battery that weighs another 15.
And you can weld on it. 8) This bike was a Schwinn, a $100 buck coaster brake bike. With a bit of welding, it now sports 7 speed rear gears, and dual disc brakes. Couldn't have made this from an aluminum bike like the electra townie.
But one of the best bikes in my garage without a motor, is a ladies electra townie.