had a 84 FJ60 with mild build (lift, tires, interior, desmog, rear locker, etc).......now have 100 series (bumpers, winch, lift, tires, interior, etc). I miss the ruggedness of the solid front axle but do not miss the never ending list of things needing work or replacign on a 28 year old vehicle that was bought new by my aunt, sold to my father and then to myself.....no rust but smog hoses, clutch, flywheel, gaskets, etc all add up and it is always something. If you have the room and the money as $10k is just going to get you started on a FJ60 built up with all the stuff needed....
The 100 series is just reliable...mechanically and as an offroad platform. We have a little offroad area called Uwharrie near here....took every trail there in FJC, FJ60 and UZJ100....from mild to extreme. They were all successful with different levels of difficulty encountered.
FJC....modern, new, decent on all terrain if you get package that includes both rear locker and ATRAC...but not a lot of room if you carry lots of gear plus a dog or kids...single or just a spouse it is fine but I was maxed out internally and on baja rack doing fj summit from east coast couple years ago.
FJ60....reliable rugged workhorse...age was catching up with every seal, bearing or gasket needing replacement....flywheel needing resurfacing and new clutch first time since new in 1984 was great...bad was flywheels are not carried by Toyota anymore so everything is used or very expensive if you get one that was horded by Manafre or SOR. Think I spent $8000 in first year with tires, repairs, etc. Great offroad vehicle but it needs to be driven to keep it working nice...not sitting for a week or month between outings of more than an hour drive. Comfort is not a strong point.....for daily driving...drove mine from charleston to mountains regularly...to work daily (40 min each way) and to Wash DC a couple times on business.
UZJ100- has cv axles up front which are somewhat weaker than solid axle in precarious situations with lots of heavy duty traction and steering needed. It is slightly larger than the 60 series for tight trails....but turning radius is tighter. Other than that I have no other minuses......I have driven every single trail my peers have driven for similarly lifted and equipped vehicles no matter if 55, 60, 80, FJC, etc. I have not attacked Kodak Rock but would need full skids and maybe 35s to do that and have a spare CV Axle ready to install just in case...yes I carry a spare just in case.

Otherwise the ATRAC is all I need.... THis past weekend I was going up trails easily that even locked vehicles had some difficulty...though we know it is combination of driver experience and vehicle capabiltiy that makes things happen.
Overall, the 100 series has a larger fuel tank...is larger inside....is built very solid with attention to detail...is very comfortable no matter the conditions and is a VERY VERY capable trail truck in all but maybe 2% of conditions you will find other similarly equipped vehicles. It wont do Tough Truck Challenge without major mods....but for expedition, camping, trail riding, and occasional rock duty...it will perform as good and sometimes better than others out there. The engine is super reliable....tranny has had some issues on earlier models but the dozen or so I have heard of pale compared to number of rigs out there on roads worldwide.
One negative is when it is 28*F outside and your buddies in 40, 55, 60 are warming up their vehicles for the first obstacle on the climb.....you need to remember to turn off the seat warmers so you dont have that annoying bead of sweat trickle down the crack of your butt and tickle you just as the trail calls for your total concentration and you cant reach back and rub to stop the tickling sensation.

Yes it is dangerous but owning a UZJ100 with heated seats are not for the faint of heart of determined mind to ignore such distractions in times of austere conditions.
Get the UZJ100 unless you have enough to spend another $10k after the initial upgrades to keep it reliable on the road and off after the initial build due to the age and smaller availability of some parts...smog devices required some states are not available new, some drivetrain parts, etc.