I strongly agree that you should buy something you should try out. A lot of the cheaper bikes may be perfectly fine, but some of them can only be ordered online. I ended up with a 24" Pedego Boomerang. I am only 5' tall, and was able to try a 26" and 24" and found the 24" fit me better. Pedego is an expensive choice, but they are well made and a lot of the stores rent bikes or let you take a trial ride of several, which i think is important.
I got the less expensive 52V 10.5Ah battery, but it takes me 30+ miles, which is as far as I would ever want to go. As I posted earlier, I got an electric bike because my knee would swell up on just a mile or two on a regular bike and I would have difficulty walking the next day.
If you cannot get a test drive on a bike and want to order one by mail, you might want to ask someone you know if you can try their bike out. I am a little hesitant to let anyone try my bike unless I know that they are a very skilled current bike rider because I let one lady try mine, and she fell and broke her wrist!! I also suggest that you try a bike out without the battery for the first time, THEN, when you feel comfortable with the weight of the bike, try it with the battery on.
I paid $2,700 for my Pedego, but have barely ridden it, and am going to move to a three-wheeler electric bike because at age 81, I don't feel stable on it. It is for sale for $800, if anyone is interested, but I am currently in Michigan, headed through Canada to the northwest.
FYI - Even with the less powerful battery, my bike can easily go 25+ MPH and at least 30+ miles. Frankly, I wouldn't want to go faster or farther on a bike trail.