It mostly depends on what I am doing and where I am
My butt plugs tend to be much smaller than my dildos, so if I want a good fill, I'll bring out the dildo.
If I want to leave the house, the butt plug is basically designed to be discreet and comfortable, so butt plug it is.
I don't actually like being thrusted by anything, so that does not factor into the plug/dildo question. I will just keep the dildo in without thrusting.