For me, the biggest difference that matters is the horsepower, driving noise, and aesthetics. People say that the 100 drives better on the roads due to the IFS, and maybe it does, it's just that I haven't noticed a big enough difference to take a 100 over an 80. Counterpoint is the live axle of the 80. Again, if you plan on doing serious wheeling, the 80 will win more times than the 100. But if you don't do the more hardcore stuff, I don't think you can go wrong with either. I think the 80 looks better, but the additional horses of the 100 will allow you to go higher and faster (think driving the dunes at Silver Lake Michigan).
Last thing to consider is vehicle noise. I think the 80 is a noisier vehicle to drive than the 100, especially at highway speeds. I sometimes take people who suffer from migraines offroad, and in an 80, they need to wear ear protection or they will be in pain. So for me, a 100 wins as a DD.