PoSign (XBY) vs. DPOS (EOS)

[xenon01]

Both PoSign (XBY) and DPOS (EOS) are often considered to be better than PoW and PoS.
However, I could not find a comparison of PoSign and DPOS.

Does anyone know the technical differences, benefits and drawbacks between these two consensus technologies?

As far as I know a 51% attacks are only possible with DPOS, but not PoSign.