I personally think digital scales are more accurate.
I think manual scales can lose their accuracy if they're not kept up. When I was wrestling there was a tournament where we knew we could be a little over and still make weight because their scales were light.
I'd weigh in at 170 on our scales and then be at 168 on their scales, so unless I lost 2 pounds on the 20 minute bus ride, i'm thinking their **** was light.
Theres no cheating digital scales though.