I personally liked RE5s inventory system overall which is funny because I thought RE5 was pretty ok, it's definitely not my favorite. The reason I liked it was because, aside from being pretty simple, I feel like it had the best functionality (in my experience of the franchise). I liked how I could go into my inventory and reload all my weapons and mix my herbs in like 2 seconds flat (I'm not exaggerating btw). I had that down to a science and I loved it, especially as the action continued around me.
Second to the RE5 inventory system, I liked the REmake2 inventory. It was very neat, and unlike RE4, weapons and items have a predictable size as far as how much space they take up in your inventory. I suppose by default this includes R3make, but I didn't like the fact that some of your inventory space is bull if you're not a god gamer that can beat Inferno mode without any of the bonus items.
After that, I like the classic ones - everything up to Code Veronica. I honestly couldn't tell you why, they just have a familiar charm to them I guess.
Lower down would be the RE6 inventory system. It wasn't as user friendly in my opinion.
And probably lastly would be RE4's. Not that is was bad, but it just felt out of place in the franchise to me and I hated having to buy a bigger case repeatedly. And it would aggrivate me because I spend forever just organizing it so that it looked JUST right lol.
I will say that I didn't hate any of these and to be honest it never occurred to me to rank inventory systems so this was a cool thread. But yeah, if I had to choose an inventory system, I would pick RE5.