I was late to the party myself and started with DST:SotFS on PS4, since then I have gone through DS3, Demon Souls and now going through DS1:R. DS2 is pretty widely agreed to be the weakest of the bunch. I really enjoyed it playing through for the first time in the series, but looking back I can see why people would say that. The map in DS1 is so inter-woven across the different areas, that any follow up had big shoes to fill. DS2 was a lot more linear in progress choice, but for a first time entry into the series I don't think that was a bad thing. The boss design in DS2 was also less than stellar, but the Scholar of the First Sin edition amps that up pretty well with some pretty great boss fights. DS3 combat speed was really amped up compared to the first 2, so I would probably save that one for last.
I would recommend starting with DS2:SotFS, then work into the others.