There might be different errors cropping up with different machines, but there should hardly be any difference between HiSeqs 2000 and HiSeq2500. This Blog from Illumina also claims high concordance of the data: https://blog.basespace.illumina.com/2012/11/26/high-concordance-between-hiseq-2000-and-hiseq-2500-data/

I would be more concerned to compare HiSeq and NextSeq/NovaSeq data since the sequencing readout is different, or Illumina and Ion Torrent machines where the whole process is different

The differences between different sequencing machine models are the quality of that data and the applications that will support it.

There shouldn't be any difference between these two platforms. Just be informed about read length if you planning to pool the data.

there shouldn't be much difference in these two models except for read length and total throughput, i think...