i'd say strangle or poison, something that isnt messy or gets blood everywhere.
then i'd wrap the body in blankets and then i'd dump the body down an abandoned mine shaft, or dig a grave in middle of nowhere and bury it.
But if i had to get messy i'd shoot em in back of head, take em to the bath tub and chop up their body parts, then i'd bury the body parts in different places spread across a 100 mile area in middle of no where.
either way i'd plan it out and make sure to never get caught