I like rpg tetris in single character rpgs. But I prefer the list or icon variant in games with larger groups. Juggling items between the backpacks of characters of the same group is boring busywork.
I dunno, I often find it conceptually easier to keep clear each member's role in the team if they have separate inventories (although of course it's mandatory that you should be able to easily move stuff between inventories). It depends on the game though, whether that feels right or not.
Having said that though, the best inventory system at the moment, for me, is PF:WOTR's general inventory with the inventory mod. You have useful tabs (weps, armor, accessories, etc.) and automatic stacking from the base game (with easy separability), and you have easy text searchability and a number of useful filters (e.g. "usable without UMD" "all unlearned scrolls", etc.) from the mod.
Inventory is always a balance between functionality for the guy sitting in the chair, with the retention of some kind of immersive level so that it still feels psychologically like you're moving stuff around in backpacks or whatever.