Whatever you can get your hands on. Once whoever breaks in sees you're armed it's a scramble for the door/window.
I have a CZ shadow because that's what I shoot IPSC with, but even a blank gun works 99% of the time.
Really? A starter pistol? Where are your stats that support a blank gun stops 99% of the intrusions?
A few years back a fellow competitive shooter dispatched two people with an Olympic-style .22 in a very publicised case where two thugs were beating his brother (a bar owner) for the days cash.
It took a single shot for each.
It is all about shot placement; pumps or switches? Hips or heads?
When you start talking calibers it's the wrong discussion. You have to use whatever you can shoot well enough under pressure.
It is the wrong discussion? You provided the statistic that 99% of events are handled by a blank gun. What happens when that 1% that the intruder cares not for what he hears, he needs whatever he can get his hands on to make money for whatever ills him/her? If you're shooting down a hallway in the dark, how will you know where to aim? Your hope is that the caliber is big enough to do some sort of damage to stop the intrusion.
For home defense, the best thing you can have is a 12 GA, with #4 shot. The funnel of doom works in your favor.
Otherwise that gun is a liability and you're a danger to yourself and society.
Better to have it and not need it, to need it and not have it. And that is why, although not a requirement, a person should train often to keep the edge sharp.