Size vs weight when expediting

Q1) What the best for expediting
Weight or size?
for example cargo van is only 10ft length but can haul more lb
16ft box truck on the other side has more space but less payload

Q2) if my gvwr is 12,000 and my truck+ the load I’m carrying weight 9k. Would I need to use ELD? My truck is rated above 10k but my actual total weight is 9k. Do I still have to use ELD?

Q3)when expediting, what should I go for? Cargo van or box trucks?

 

Cargo van is limited with size and height but has higher payload capacity

the same truck with 16ft box has less payload but more size
Should I go for 16ft box truck Chevy express or Chevy express Van?

 

It would be better mileage too