I'm probably preaching to the choir - or maybe beating a dead horse - but I'll throw in my .02.
I currently own a '03 Dodge Ram 2500, Quad cab, short bed, diesel 4x4, as well as an '07 Toyota FJ Crusier. I DD the Ram whenever I can't take my motorcycle for some reason. Before the Ram, I had a 94 regular cab Toyota Pickup, and an '88 4runner.
I've had the Ram for almost 11 years now; bought the FJ last year thinking I wanted something smaller, lighter, and more maneuverable for the sometimes-tight trails and forest roads here in Michigan.
Although the FJ is great for what it is, a decent off-road toy and fun DD, I've found I actually prefer the Ram, and will be selling the FJ in the next few weeks.
Pros for the FJ are smaller, lighter, and more nimble, and superior Toyota build quality. It's definitely better in the off-road performance sense, but I don't rock crawl or hard-core off-road. The Ram has gone everywhere I wanted it to, as long as it fits. Pinstriping adds character.
MPG is a wash, more or less. They both get 16-18 MPG in mixed driving, but the Ram does better on the highway. Gas is cheaper than diesel, so right now the FJ is less expensive to fuel, but that's with it unloaded, and basically stock with slightly upsized tires (285/70R17 vs 265/70R17). The Ram has stock suspension, but has 35s currently, and has room to fit 37s.
Full-size Ram Pros: payload (mass and volume), towing capacity, interior room (seat 5 easily, 6 in a pinch), road presence, visibility, winter performance (even in 2wd vs the awd FJ; 4 tons makes for good traction), the list goes on.
For my needs the Ram is more truck than I need, but I like that it's under-stressed. I did the clutch on the FJ recently, and everything about the chassis and drivetrain (frame, suspension, axles, transmission, etc...) seems tiny and fragile by comparison. Some of this is certainly perception, but the HD Ram is very obviously built to work and take abuse, while the FJ is substantially less so.
I've gotten so used to the full-size I just can't get comfortable driving a smaller, light-duty vehicle anymore.