Standard Grid has more nodes, but each character kinda has its own section on the grid, whereas Expert Grid gives you a bit less nodes, but all the characters start near the same place in the middle. This gives you access to other character's nodes early on, pretty handy.
So if you want 'more stats', go with Standard.
If you want 'more freedom' when building your characters, go with Expert.
Just be aware that you don't NEED the extra stats from Standard Grid. You can beat the game perfectly fine no matter what you choose. It's just your own preference.
Personally I always go with Expert, because I love making versatile characters.