sigh... I wish these bike shops would GET A CLUE!!!

Greet everyone, offer assistance, and give space if that is what is desired.
It's really quite simple.
I'm sorry that you had such and issue with shop B. But as a small lbs owner myself, I think shop A may be your best bet.
All of the bike brands mentioned are fine bikes. Heck Giant MAKES most of the bikes for other manufacturers, so chances are the different bikes were made in the same factory!
As for the bike, I do recommend double walled rims. And as for the big ol saddle- steer clear! I'm a big girl too, and my flat bar road bike has a wider saddle than I am used to. It chafes me after about 40 minutes on the bike! Not fun for us ladies with larger bottoms! I warn customers about that all the time. The adage I use is "sometimes less is more".
I must also say KUDOS to you for hanging in there with shop b!
I get people in the shop all the time worried that they are too big to ride. I do my best to get them going, because really most everyone can ride. Yes there are a few exceptions, but even those have options.
Good luck in your search for the perfect bike! It is out there. But I do recommend riding as many as you can. AND get the bike that FITS! Fit is the key. Hopefully lbs B has some kind of system to measure you to make sure you get on the right size bike. (otherwise go to wrenchscience.com and go into their fit gallery and measure yourself).
cheers!
Denise