I've spent the past few years trying to figure out exactly this question, driving around all over the place in all kinds of gnarly weather, always camping in my vehicle. Because I'm kind of a restless buyer/seller, and because I sometimes go early and rent a car and drive around places when I go to conferences for work (i.e., instead of staying in the hotel), in the last seven or eight years I've camped in the following:
'99 Jeep Cherokee 4WD (just a couple times--fine, but not quite long enough for two side-by-side)
'06 Prius (surprisingly practical for an 8,000-mile car-camping trip; not much less flat space than the Cherokee, though I did have to move plastic luggage bins outside and the dogs had to sleep up front
)
'89 Toyota long-bed 2WD (comfy, but squeezed tight on a mattress under the canopy in the pickup bed; not so good in sand
)
'79 Chevy crew cab 2WD, then converted to 4WD (one several-thousand-mile trip before the conversion, one after--I loved that truck, and it was comfy as hell sleeping on a big mattress under a canopy in the back, but I didn't love getting 11 mpg even after I swapped in an automatic with OD; also took a several-thousand-mile trip in the same Chevy with an Alaskan pop-up camper in the back, which was mostly awesome, but again: mileage [also, the camper was from the 60s and it was a huge pain in the *** to lift and lower, especially on one long solo trip])
'91 VW Jetta Ecodiesel (god I love this little car, and I love zipping around getting 45 mpg, but I am cramped all to hell every time I sleep in there, which has been pretty often, all-told)
'94 Nissan king-cab 4WD (very comfy with an over-the-rails cab-over camper--a queen-size mattress for me and my lady up top, and plenty of space for the dogs or another couple down below--but pretty poor gas mileage with that hunkachunka blowing every which way once I got on the freeway; after ditching the camper for a canopy, still only 18 or 20 mpg at best, and feeling a little claustrophobic)
'11 Dodge Durango(?) AWD(?) (roomy, comfy nice rental car for 1500 miles around Anchorage and Seward Peninsula and such)
'12 VW Passat diesel wagon (exceptionally roomy rental car getting amazing mileage for 1500 miles around Norway, and having AWD, to boot!)
'84 GMC Suburban 4WD diesel (loved her, though I never got such great mileage as others--16 mpg at best--and her engine quit on me a few hundred miles from home out on Whidbey Island, in WA)
'11 Toyota Yaris (yuck)
'03 Chevy Suburban 4WD (************* perfect, and getting a size-respectable 16-18 mpg, too)
With ten feet of flat space in the back, and the option to keep the middle row of seats up without having to take my memory foam mat out or really rearrange much of anything, the 'Burb is--for my money--by far the most practical camper of all the vehicles I've owned or rented. Especially this '03 (which I bought with a 30K-mile-old reconstructed title, and thus got a great deal on), which really has it all: what is effectively AWD for those long stretches of semi-icy, semi-dry road up and down the mountain when I go snowboarding, but true 4WD for stepping through mud and deep snow with relative ease; decent mileage for a bigger rig; a cavernous and (in the current instantiation, much more than the '84
) very pleasant interior; readily available and reasonably priced parts; and just WAY WAY WAY warmer and more comfortable to be in for winter sleeping than the bed of a pickup. I was up on Mt. Bachelor in Oregon the other weekend, and it was 8 at night (minus whatever the wind chill was), and--apart from some blanket-grabbing by the dogs--I was legitimately warm enough.
Anyhow, my two cents
. I hope that whatever you end up getting, you love it!
