The bike industry today is very homogenous.
Similar money buys you comparable bikes regardless of brand.
One has better brakes, another has better gears.
Bikes in the same price range from different manufacturers are mainly different rather than universally agreeable better or poorer.
The challenge is to find which one that fits YOU, and your preferences the best.
Failing that, finding the shop that treats you best.
First I'd recommend a reality check.
Weight is mainly lost at the table, not along the bike path. Calories are so much faster eaten than used up, that any serious attempt at weight loss pretty much has to start with controlling what you eat.
I ride for something like 2.5 hours daily, at mid/high intensity, and even I have to watch what I eat to avoid gaining weight.
But exercise helps, sure.
Drop bar road bikes are a bit of an acquired taste. You need to be OK with the forward lean etc to get along with them. And as a rookie rider, it'll be difficult to separate what aches that comes from simply not being used to the position and activity, and which that comes from the bike simply being a poor fit for you.
I am by any standard an experienced rider, but I can't ride every bike in tolerable comfort.
An old back injury has left me with reduced mobility, so I need to set my bikes up "shorter" than recommended. You may have a comparable issue.
Many think that wider, softer saddles is the way to go, which it generally isn't.
Soft saddles are like walking barefoot in sand, cushy and supported at first. But eventually the arch of your foot will start to get sore. The sit bones, the areas that are truly supporting your weight, are rather small. Each about the size of your thumbprint. They will get sore if they're not used to the job.
Bike saddles are only comfortable when compared to other bike saddles.