Rotigus/unclean one with nurglings usage or using points for knight for 2000 point list?

So I asked question regarding daemon allies and got great replies.

I was told I could use greater daemons and daemons like nurglings being best. I was told even rotigus could be used?

So in 2000 point game, would rotigus/nurglings be a good combo with large knight lists (or even small knights with some large). Im wondering if rotigus OR generic great unclean one with nurglings would be better points wise than what I would get for equivalent knight?

Thabks for help. For reference I only play against 6 players, all marines and 3 dark angels.

Thanks for help!