You have to define your budget and your intent. 80's can be modified (ie lifted more) so larger tires are an option on 80's and not so much on 100's. Also don't be fooled by the price of the purchase. Most 80's now require extensive refurbishing to make them reliable. They do go forever but not on their own. The initial savings on a 80 will be chewed up in maintenance in a hurry. Ask me, we do this on a daily basis. They are an awesome platform, but they are not immune to breakage and wear.
If you do your own work, then that is not so bad. If you rely on a shop, you are going to spend some serious $'s.
I love both, but for most people, if they actually evaluate their realistic requirements, and not the dreams while reading Overland Journal, they need much less vehicle than what they think.
Case and point, you need a solid axle, why? I am not going to debate the merits, but as yourself if you really need it. In some cases people do.
I have had both 100 with SAS and now a 80 with a 4.7L v8 and every other combination in between.
I can not really choose, but if you are not needing a solid axle, then the 4.7L v8 is a really nice upgrade over the 1FZFE 4.5L. The IFS stuff is going to require more maintenance when being abused on a daily basis. That is just fact. Is it weak, no.
I put it like this. If you are going to drive through Africa I want a solid axle. Relatively small spare parts load to fix pretty much any situation. Hit a donkey sized pothole and things can normally be straightened and hammered and welded into place on a solid axle truck. Not so much with a IFS. Drive 500 miles and do a little weekend outing on some dirt roads in the US, I would take a 100 series.