I haven't really used this much but it appears to me that the difference is:
"Non-destructive slice" creates a 'list of slice regions' that resides (is stored) with the sample.
A sample with a slice list that be shared by many programs.
"Pad parameters" creates a 'list of slice regions' that resides (is stored) with a program.
Each program gets their own slice list.
Anyways, so why are there options if one is better? I don't think one is arbitrarily better. For any given situation, one may feel better suited. So, use the right tool for the job.

If you want to have different sets of slices from one sample, use "Pad parameters". On the other hand, if you want to manage a single set of slices across several programs, use the "Non-destructive slice", which enables you to change the slice points anywhere and it's audible everywhere. Remember that OTHER parameters are still kept separate between the programs using the same non-destructive slice, e.g. pitch, etc..