Correct case for each reserved word in SQL Server?
So,

Writing it as an answer for anyone else who might need this in the future-the answer to this question is described very nicely in the Why I use lower case for data type names (now) blog post from Aaron Bertrand.

As he explains in his blog post, this is important when using different database collations from the default one, for example (from the blog):

Considering this database:

CREATE DATABASE floobmort COLLATE Latin1_General_BIN2; 
GO
USE floobmort;


The following query will provide an empty result set because "That comparison tries to compare N'INT' to what's stored in the table, N'int', and because the comparison is done using a binary collation, it returns false."

SELECT system_type_id 
FROM sys.types 
WHERE [name] IN (N'INT', N'VARCHAR');