Personally we found the GX provided more headroom and legroom than the 100 in the first 2 rows. The 3rd row on the GX is very limited, but the 100 is not much better. The 100 is wider and provide more interior width.
The cargo area on both are the same in total volume, but the 100 probably has more usable space,as it is wider vs higher on the GX. On both the dorky 3rd row need to be removed to get any real cargo space.
We looked at the 05 100 vs 05 GX when we bought back in 05. Both have great interiors and feel very solid. Personally I don't like the pre 03 100 interiors and think the 03+ 100s are much nicer inside.
Both of them ride very nice as well. It is preferable to get the GX with the KDSS suspension for improved handling. The GX does feel lighter and easier to maneuver around town, also much easier to park. Thus in the end it won as the

was using it mostly. The 100 is definitely slower to respond in turns, harder to park, etc but the highway cruising felt a tad better than the GX.
If you however plan to modify the truck down the line you will be better of with the 100. There is very little for the GX apart from suspension parts and bling, armour will be custom for the most part on it. 100 seems to have much more useful aftermarket options for offroad use.
Personally I really like both, but the GX won out as it was much more useful in everyday use and driving. The

also liked it much more
