Assistance on Upper Body Days

What would be better?

Bench 5/3/1
Dumbbell Bench

Press 5/3/1
Dumbbell Press

or

Bench 5/3/1
Dumbbell Press

Press 5/3/1
Dumbbell Bench

or

Changing every cycle between those options?

It’s really doesn’t matter because weekly amount of work will stay the same. It’s up to you which template you like more.

There is nothing “better”. Just different.

What is better is setting PR’s.