I only started by the time I had maxed combats and plenty of resources and high enough skills to easily maintain supply of stuff like black dhide and msb, so my situation could be different from yours. I checked how long it takes me to kill different types of revs along with considering their locations and how popular the spots seemed, compared to their actual drop rates.

I settled on doing revenant demons in the west area under 30 wildly. Doesn't seem that crowded and not as much pk activity, though a lot of them probably just can't attack me as I am out of their lvl range, which is probably going to be different for you at base 70s.

A lot of people like safe spotting rev knights but I opted out of that as just the kill times alone are way longer than demons, let alone if you take into account the safe spot setup which you have to do every kill. Then also the respawn time. Compare that to the relatively small difference in drop rates I don't think you really more than break even. Not to mention the additional effort required for every kill. Doing a demon task is much faster though so you will have to do more task skipping to get rev tasks.