You should use decimal(p,s) in 99.9% of cases.
Percent is only a presentation concept: 10% is still 0.1.
Simply choose precision and scale for the highest expected values/desired decimal places when expressed as real numbers. You can have p = s for values < 100% and simply decide based on decimal places.
However, if you do need to store 100% or 1, then you’ll need p = s+1.
This then allows up to 9.xxxxxx or 9xx.xxxx%, so I’d add a check constraint to keep it maximum of 1 if this is all I need.