Automatic Transmission Service/Flush on 2006 Buick Rendezvous

In the Owner's Manual for my Rendezvous, I find that at 50,000 miles I should have the automatic transmission/transaxel serviced. On all reports from oil changes and the like, I have never had any mention of any problem with the transmission and we are not experiencing any. I now see that I can get an transmission "flush" or a transmission "service". I do not know the difference except that, I think, the service includes the replacement of the filter.

Which is the better choice in this situation? Is it necessary to have the filter replaced at this point?

Asked by for the 2006 Buick Rendezvous