If you room is fairly small and every inch counts.
If you want to use trundle bed or storage bins.
If you worry about obstacles.
If you like tidier look.
If your prefer to climb at ease, angle ladder is a better choice over vertical.
Staircase is the safest way of climbing up or down a bunk bed.
If safety is your main concern.
If you have extra 20” or so by 42” extra room for stairs.
If you have healthy budget.
A good compromise to vertical ladder.
You have more foot and hand hold to operate.
Very small footprint.
Can put storage under bunk with easy access.