completely individual to the person.
Otherwise everyone would pull sumo in competition right? But they dont. For me sumo actually makes the ROM greater, and makes the weight hard to both get off the ground (because it is extra deep) and also to lockout, because my optimum grip with causes hands to hit my hips.
I spent quite a bit of time experimenting, what I can pull for 1 with sumo I can pull for 3-4 conventional.
Some people recommend starting with the style you find most difficult at the start of a training cycle and switch to your optimum one towards the end when things are tough.