To order the DF Asha'man in WH fits best, IMO, because Demandred acted weirdly, especially by wanting someone else to kill Rand, when we know that he actually desires to do it himself.

Besides, it's the best comparison to Aran'gar's thought in KoD that someone played her own game now by apparently disguising as Sammael, i.e. disguising as a concrete, identifiable Forsaken. The idea of such a disguise is that you could achieve to kill Rand, but even if not, you might at least confuse others and conceal who truly gave the task & discredit other Forsaken of acting against the DO's/Nae'blis' orders.

We know that Aran'gar considers Demandred to be very dangerous, but also wants Rand's death. Therefore it makes sense for Aran'gar to give DF orders to kill Rand in a Demandred disguise (since Aran'gar uses saidin, she wouldn't take a female Forsaken disguise, when meeting the DF Asha'man). Even if the DF fail or are captured, they could e.g. only tell Rand or Moridin that they were ordered by Demandred. And then Demandred might get a problem..

I doubt that Aran'gar would care about Masema, since she is concentrated on the Rebels. On the other hand, Rand's death is always desirable, as Aran'gar states herself in KoD.

Others suggested that Aran'gar was Slayer's patron in WH, but I believe - for various reasons - that the patron was Osan'gar.