Are A bodies more popular than B bodies?

Mostly repeating what others have said already, has more to do with prices of B-bodies being too high for reasonably-minded people on a budget to afford.

I originally wanted a 68-70 RR but "settled" on my '70 Duster. Being a function-over-form type of guy I found I like this car better anyway. It's just easier to make them fast and handle well because they're smaller and lighter. B-bodies are super sexy, I've come to really love the 71-74 Plymouth B-bodies but they're LARGE. And really I think the 69-73 fuselage C-bodies are just as beautiful if not more so, so if I want a "big" Mopar I'll probably get a C-body.

At the end of the day once you get past the exterior sheetmetal they're all the same car just with different lengths and widths. In reality C-bodies are the most unique design and engineering-wise since at the time they had the highest volume of sales and brought in the most profits for the company. A good number of parts are shared between A, B, E-bodies but C-bodies use a lot of unique stuff.

After I manage to sell my truck and get a comfy modern daily driver (looking at 2004-08 Acura TL) my next old Mopar project will probably either be a C-body wagon or a mid/late-70s B-body like a Cordoba or Magnum. I want to screw around with a big-block car but I can't justify spending thousands of dollars more just because something looks 'cool' and says "Charger" or "Road Runner" on the side. I'd imagine there would be less flak from the purist crowd also if I happen to swap a Mercedes OM606 straight-6 turbodiesel into a C-body wagon lol.