I think the best expedition platform is whatever you have at the moment that allows you to get out there and see the backcountry. I was cruising around the trails of southern CO and had a (what appeared to be) stock Subaru Legacy pass me, and a few Honda Civic and Accords! I even saw a minivan but judging by the look on the drivers face I think he realized his mistake. I had to do a double take several times. Up until recently our adventure rig was a 1999 F-350 diesel Long bed dually, the 10k lb land yacht. That thing has seen more "off road" than your average mall crawler lifted Jeep. I have taken it places Im sure it didn't belong but it made it! It made it while hauling all my tools, gear, food, and still left tons of room for a very relaxing trip down the highway. The truck has since been retired to just heavy hauling down the interstate when we picked up a new adventure mobile.
After our first big trip to CO and UT for some trail driving my wife quickly realized the truck was great but too big for some of the trails. A good friend loaned us his '03 4Runner for our next big trip and she loved it. After that she gave me the thumbs up to find another toy for the garage (which may or may not have been part of the plan hatched by my friend and I to use his 4Runner).
My criteria was simple. Had to be: reliable, daily driver, room for an expanding family, smaller than the truck, under $12k, good aftermarket support, and the number one determine factor was the wife had to like it. Here is the list of vehicles I considered:
100 Series Land Cruiser - Brother-in-law made me a deal on his 2000 that I could not refuse. Took the first plane to Boise and drove it home
80 Series Land Cruiser - Looked at several, but they were in rough shape
4Runner (any year, but preferably 3rd or 4th gen) - Couldn't find the "right" one for my budget
Tacoma (any year) - Had a hard time finding a solid clean used one that wasn't outrageously priced
Jeep JK - Too $$$ for me but I looked anyway
Jeep XJ - Found several, almost bought one but it sold before I could jump on it
Xterra - Found several that were decently priced, but the LC deal won me over
Disco II - They all had one too many problems for my liking, but I decided to give them a shot and take a look
LR3 - I really liked, but couldn't get past the potential headache of all the electronic nannys later down the road
Another 7.3 Super Duty - Has been the most reliable vehicle I have ever owned
I'm not going to lie, I had my hopes up of finding a LC the whole time. I had driven one more than all the others and really liked it. But I tried to be open minded and really consider every one. One thing I really like about the LC I brought home was it is clean. I really wanted a vehicle that was clean and had been maintained better than average. I have never really worried about miles as long at the car has been well maintained. MY truck has +355k miles on it and I wouldn't hesitate to drive it across the country tomorrow because I know its in good shape. My recommendation would be to find something that has been taken care of. As mentioned by other they all have their pro's and con's (some more than others). Any rig when taken care of and properly operated will last and take you anywhere. Some have more curb appeal than others but looks can be deceiving. I just can't say I would recommend buying something new to go drive somewhere that you're most likely going to beat it up.
I agree with a lot of the above logic.
I have a strong Landcruiser Bias. I've put about 100k miles on what started out as a neglected and tired FJ40. There is a reason they have a reputation for lasting. It's 42, has about 250k miles on it, can be fixed anywhere with basic hand tools, and it has taken me to hell and back. Yes, the motor died at about 200k miles... it had been driven by at least 2 POs with no air cleaner, and yet I still drove it home with a knocking rod.
You'll need to narrow your priorities... you've got too many opposing interests.
-My 40 will do awesome on tight trails, but space is at a premium, 80 mph is scary, and it's a tractor that likes to visit gas stations... It also tows well, but not a bigger trailer on the highway.
-My E350 AMBO with a 7.3 is beautiful to drive on the highway, has tons of space, is reliable, and no worse on fuel... but it can't do a tight trail... but it'd tow 10k lbs.
You're probably looking for something in between. I'd want something I could sleep in if it was crappy out or I couldn't find a campground that wasn't $85/night. An FJ Cruiser might be ok for sleeping in, it'd take a RTT, but they still like fuel stations.
An 80 Series Landcruiser with a JDM Turbo Diesel, and a RTT, would likely be at the top of my list... Just hard to find, and not so stock... and staying stockish is wise for what you're looking at doing.
Or a 7.3 Diesel Van with a U=Joint 4x4 conversion, Lift, and 35s... it'd be good on the highway, be big enough to live in (solo or couple), would tow, be ok on fuel, be reliable, and parts are easy to find... they wheel well, but you might have to pass on the tightest trails... but you did say most of your driving would be on the highway.
Pick your compromise, and enjoy the adventure... you can't have it all.
