Hi dgdi,
like already mentioned in the last post, it shouldn't matter much, but there are some significant differences between the file formats, which you find listed here:
TDM versus TDMS - LabVIEW 2013 Help - National Instruments
http://zone.ni.com/reference/en-XX/help/371361K-01/lvconcepts/fileio_tdms_tdm/
The main difference is that TDM only supports Windows OS while TDMS also works on other operating systems, which becomes important when you want to include platforms like the cRIO hardware.
Buttomline: I would recommend TDMS, when you can live with the fact that you can't delete Data from the file with LabVIEW, you have to use DIAdem for that.
Best, Niko
Niko NR
Systems Engineer, National Instruments