I have a DPE like the one you describe, and would never go to anyone else if I could help it.
That personal relationship goes a long way, both for your comfort level and the amount of slack you you might get in the event of an un-characteristic screw-up on your part. The guy you know has a baseline on you, and may gloss over a screw-up based on your previous good performance. The new examiner doesn't know you, and if you goof once, he has to assume that you are no bueno and pink you.
Also, the more cynical answer is that there is an unwritten quota for DPE's...the FSDO simply does not allow them to pass everyone.
The guy who knows you will not pink you just because he is behind on his quota that month.
If you use your guy, be sure and get some gouge as to how he conducts the checkride in question...maybe call him and ask him.