What are 3 ways to get a count of the number of records in a table in

1) Count(*) and Count(1) are same but Count(1) is faster so use Count(1)

SELECT Count(1) 
FROM   TableName

2) We can use SQL Server catalog views with the following dynamic management views:
    sys.tables – populates the list of tables.
    sys.indexes – populates the list of indexes of the table.
    sys.partitions – populates the rows of each partition.

This approach is faster than the COUNT function. To get the count of rows, run the following script:

SELECT a.NAME, 
       c.NAME, 
       Sum(b.rows) 
FROM   sys.tables a 
       INNER JOIN sys.partitions b 
               ON a.object_id = b.object_id 
       INNER JOIN sys.indexes c 
               ON b.index_id = c.index_id 
                  AND b.object_id = c.object_id 
WHERE  a.object_id = Object_id('tblCustomer') 
       AND c.index_id < 2 

3) The sp_spaceused procedure along with the rows count provides the following details:
     Name – the Table Name
     Rows – the Count of the rows in a table.
     Reserved – the total reserved space for a table.
     Data – the total space used by the table.
     Index_size – the total space used by the index.
     Unused – the total reserved space for a table that is not used.

The syntax is: EXEC Sp_spaceused 'database_name.schema_name.table_name'
Example query:EXEC Sp_spaceused 'WideWorldImportors.dbo.tblCustomer' 

select count(*) from tableName

select count(1) from tableName

select count(PKColumn) from tableName

Please check the execution plan for each then select the good one.