DFSSLOGP DD is for primary output SLDS dataset and DFSSLOGS is for secondary SLDS output dataset.
The purpose of the secondary output SLDS is that it is used for dual archiving.
So the answer is you can use one of these two, primary or secondary, because they should be identical.
Found this informaiton at the IBM site:
DFSSLOGP DD (for primary output SLDS)
If dual SLDSs are being created, they can have different block sizes. However, if FEOV is specified, it is ignored unless the block size of both data sets are equal and both are allocated to tape. If tape is specified, it must have a standard label. You can specify 2 through 99 write buffers.