Anyone use Personal Assistant Apps? (Best one?)

[supertom]

They're very helpful for handsfree operation while driving. Which one do you use and which one do you think is the best? I've been trying to do some research and i've only tried S Voice and Google App. I'm looking for a very capable one that has very low memory usage, and nothing that runs in the background if the app is closed (or if I had NOT launched the app yet). The google app seems to always be using 20-40mb of RAM even when I haven't launched it yet. I'm using a Galaxy S5 on Marshmallow 6.0