I'll be honest.
I did Decision maths at AS and got 16/100 in it. I hated every minute of it because not only is it boring but so repetitive and all your answers have to be in an order. It is easy to lose so many marks so quickly.
When I retook my AS maths I changed to stats and got 86/100. I found it to be relatively more exciting and more logical.
My opinion is it is worst branch of maths. I hated it with a passion. But that is just my opinion.