I personally prefer the Ford chassis in the class Bs, mostly for the front suspension but also because I like the ergonomics a bit better inside. The front end is just beefier. There is a reason that 80% of the class Bs out there are on Ford E-chassis. I won't say the GM is cheaper for the coach manufacturers, but as a very general observation, the quality of the coaches I see on GM platforms are of lower quality than the ones you usually see on Ford chassis.
I will also say (although I haven't driven or played with the imports for a long time), the last time I looked they were a stretch... meaning, they are great at building small vehicles since their country of origin uses little trucks, but they don't have much experience upscaling things to heavy use. American truck manufacturers have a very long history of borrowing from their larger chassis and a lot of experience with HD stuff. This may have changed since I was in the medium duty market, but it can mean a world of difference in how it drives and handles things like braking, cross winds, etc. The ones on the new Ram Van chassis I can't speak intelligently about having never driven one, but the Ram Van seems to be a well-liked thing. It also completely depends on how big she wants. If you're doing a 26', go Ford. If you're doing a 14', who cares. A souped-up Hyundai Entourage could probably handle that.
As far as the coach itself, I'm also a wee bit out of the loop. The newest RV I currently own is a 1999. There used to be several really good manufacturers, then RV corporations took a big hit in the early 2000s with the bubble/recession and they all seemed to switch parent companies. What used to be the cream of the crop (like Holiday Rambler) got bought (by Monaco) and their quality tanked to stay profitable.
The nice thing is, its pretty easy to use a couple quick indicators that at least suggest quality in the rest of the build.
Cabinets. Open a cabinet door. Grab it and push up and down. Most of them have the world's cheapest and flimsiest hinges. Even the trip from the factory to the showroom, they'll start showing sagging, misalignment, and fatigue. If the cabinets are made of luan with a 1x1 scab in the corners, just run.
Carpet. Nearly all will use the thinnest, cheapest carpet you can buy and it will look 5 years old after one year of a few weekends of camping. Good carpet is a good sign.
Upholstery. Leather is usually pleather and remarkably thin and cheap. Assess the quality of the upholstery and it will give you an idea of how much effort/money they put into building
The rest is just layout preference and options.