Is it best to buy skip the line tickets to see Michelangelo’s David? Going in October and not sure how long the wait will be to get in.
You can buy timed tickets on-line and then just show up for your day and time slot here:
https://www.galleriaaccademiafirenze.it/tickets/
Many people have reported showing up off season and getting tickets without issues. You need to balance whether it is a "must see" for you and how willing you are to set your schedule ahead of time. If it's a "must see" and the line is 3 hours then you're committing to standing in line for that time. That is versus putting a time on your schedule you must stick to regardless.
I don't think there is any difference in price between online and in person and and nothing exempts you from the security check line so there is no "breezing in" ticket that gets you right in.
Have a good trip,
=Tod