you could also argue mars because even if you've thought about it....considered how you feel....your final decision requres mars/action to carry it through...and you could say pluto....it's your deepest part of you....i'm sure any decision you're making is going to be linked to your pluto one way or another.
or saturn...because it's the 'skeptical' 'practical' part of you... both essential parts of decision making
and then what kind of decision....a love decision...then maybe venus
etc
decision making is def a multi part process....and with in that process i'm sure all the planets play a part at one point or another.
my gut (let's just call it moon) is def operating
my mercury is def doing the analysing
my pluto determines why i'm making the descion in the first place, what i wish to achive
etc.
idk