Do transactions with null data take longer to confirm?
Not all miners accept transactions with null-data (OP_RETURN)
outputs
Not all nodes relay such transactions
Are you sure that your null-data transaction is standard (for clients 0.9.x+) ?


UPD: your output is 6a74686973206973206120746573740d0a and decoded to:

OP_RETURN // 6a
OP_DEPTH  // 74
OP_ENDIF  // 68 ... oups!


This is non-standard output. Because null-data output should contain only one OP_PUSH operation, not an arbitrary bytes