I always assumed it was Obi-Wan especially in light of TCW. Padmé technically has known him for longer than she has Anakin, he’s expressed a distrust of the Chancellor openly, has the confidence and trust of Padmé’s friend Satine, knew about and kept the secret of Anakin and Padmés relationship, and is a high ranking member of the Jedi Council.

It’s not massively apparent in the final cut of RotS or in TCW (thanks to the Return to Mon Cala arc being cut) but, by the end of the War, Padmé is really having trouble with finding herself on the opposite moral side to her oldest adviser/mentor and her husband. A build up of that conflict would have gone a long way to explain exactly how quickly Anakin assumes Padmé and Obi-Wan have teamed up against him when they all get to Mustafar.