Ask yourself these questions: Can I do my own mechanical work? Do I like to spend a lot of time wrenching?
If you answered yes to both, go for an 80 series, or a 60 series if you don't need to tow much. If no, look for a 2000+ 100 series (stronger front diff)
Here's my reasoning, and I own both a 84 - 80 and an 86 - 60. You will spend a lot of time wrenching on either of these trucks. The only way around this is if you can find a previous owner who was very anal and kept up with all maintenance, and has documented it. Even then, the older the vehicle the more constant upkeep it will need. I bought my 94 a year ago with 100k on it. I promptly replaced as many wear items on it as I could. I spent abut $1000 on parts from CDan and did all th work myself. It takes a lot of time to properly do preventative maintenace on an 80 series. Something still always needs fixed, slow or non operating power windows, leaky suroofs, rear windows, brakes, etc.
I just picked up an 86 60 series with the H55 5 speed. My initial impressions are that I love the truck, but I would rather not have it be my full time rig for family hauling etc. It too will take a lot of care and feeding, and I'm already cracking on replacing all the common wear items. I would not want a 60 without the 5 speed if I had the choice.
A 100 series is simply newer and is less of a truck. Every series of Landcruiser got less utilitarian, and more civilized. That said, 100 series can still off road fantastically from what I've seen. It will do 99% of what most people will ask it to off the pavement. It has more safety features for your family, drives nicer on the highway, gets better MPG, more room, less small things to fix (due to age).
All that said, I love my 80 and 60. They work great for me. They both have their annoyances, but they are both 14 plus years old. I enjoy wrenching on my junk, and like the ruggedness of both series. I do sped a TON of time wrenching on them though. If I was a family man, I truly feel I'd go for a 100 though. there have been many times on long road trips where I thought about how much more comfortable a 100 probably was. But I get a certain pride from driving these old machines daily, and knowing that I can drive them across the country (did it with the 80), and understand what might go wrong and know how to fix it.
To refrain, unless you really want to spend a lot of time wrenching, go for a 100 series. Being a family man, I'm hoping you have better things to do with your time than fixing annoynances. I often catch myself thinking that I could be camping or hiking instead of laying under one of my cruisers for hours on end. And all of these guys who are suggesting engine swaps, trans swaps, that will only multiply the amount of time you spend on your rig by 100.