Appropriate datatype for holding percent values?

Assuming two decimal places on your percentages, the data type you use depends on how you plan to store your percentages:

• If you are going to store their fractional equivalent (e.g. 100.00% stored as 1.0000), I would store the data in a decimal(5,4) data type with a CHECK constraint that ensures that the values never exceed 1.0000 (assuming that is the cap) and never go below 0 (assuming that is the floor).
• If you are going to store their face value (e.g. 100.00% is stored as 100.00), then you should use decimal(5,2) with an appropriate CHECK constraint.

Combined with a good column name, it makes it clear to other developers what the data is and how the data is stored in the column.