SQL Server BigInt vs Decimal
If you don't need fractions, choose bigint. In your case it will be a byte smaller:

10 digit decimal is 9 byte: https://msdn.microsoft.com/it-it/library/ms187746.aspx

bigint is 8 byte: https://msdn.microsoft.com/it-it/library/ms187745.aspx

Plus, it is faster (it has no variable part, and it is an integer type, much faster processed by cpu).