Here's my $0.02...
Campers/Travel Trailers/Toy Haulers/RVs/Etc. are a series of compromises
Even a $7MM Newell Coach has trade-offs. Obviously more $ allows you to make less sacrifices, but even in the biggest, baddest Coaches you only have 45'... that's it. And even choosing a 45' Coach is a trade-off in itself. It limits campsites, attractions and to a lesser extent roads you can use.
So, given that RVs are all about compromises I think the best thing to do is to start with a) your budget b) your must-have features. You'll pretty quickly find that cross-referencing your must-haves vs. your budget will make your decision a lot easier.
For me, when I was buying my first RV (coming from a string of 5th Wheel Toy-Haulers) I had a budget in mind, because I did not want to finance. I made my list of "must haves" and when I put it all together I liked my options in a Gas Coach a lot better than what I could get in a Diesel Pusher.
At the time I wanted to spend around $80k, we had to have a King Bed, I wanted a 36' or less, and I wanted something that had a nicer, newer luxury feel to it. We also had to have good sized holding tanks (we dry-camp a LOT) which pretty much ruled out Super Cs.
When it all came down to it, I landed on Gas Class As. In the price range I was looking I would have been going with a much older Diesel Pusher, and generally with the small 300-350 HP diesel engines. Also, it was extremely difficult to find something short that also had a King Bed. It seems that it wasn't until at least the late 2000s that Kind Beds became common in anything other than the big-dog 42-45' pushers.
Now, about 15 months later I'm selling my gas Class A and moving to a 40' Diesel Pusher. Did I make the wrong choice back then? No, not really. For one thing, my budget has changed since I'm now willing to finance. We have spent over 100 nights in our Gasser in the last 15mo, now that I really know how often we use it and how much we enjoy it I can justify the payment. Second, we still LOVE the floorplan, space, quality, features etc. of our current RV. But I simply need to pull a bigger trailer. There are those that would say I should just beef-up my Gasser (bigger hitch, trans cooler, etc.) but to me that's not the right solution. I've never towed more than my flatbed trailer with my Gasser, and it does beautifully with it. IMHO that is because the entire Coach, as a system, was designed to tow something like this (FWIW the Coach is rated at 6k lbs towing stock, my flatbed with 2 RZRs is around 5k lbs).
So, again it is all about trade-offs. I'd be 110% happy with the floorplan and quality of my current interior. But to truly get the towing capacity I now want (15k lbs) the absolute minimum size I can go is a 37' DP (things like the Tiffin Alegro Bus or Newmar Dutch Star in their 37' floorplans). I really don't want a giaaaant Coach because a) it's just my girlfiend and I b) we enjoy smaller State parks and things like that. But the 37' coaches actually measure around 39' so heck, at that point I'm almost in a 40'. Moving to a 40' gets me bath and a half (we have guests very often) and more living space.
As such, I landed on a 40' Newmar Dutch Star that gets me a 450/1250 HP/TQ ISL, a factory 15k lbs hitch and a tag axle
in a 40' Coach that will still get me into 99% of the places we go. But I am still giving up that 1% as well as a few hundred thousand dollars vs. my current RV.
PS- shameless plug/might get me in trouble but my Gas Coach is for sale: 2009 Fleetwood Southwind, Palo Alto CA - - RVtrader.com