I reckon cast iron griddle would be good if you didn't want to kill the intruder (although you probably would kill them if you hit them on the head with it). It's ridiculously heavy and would incapacitate someone if you hit them in the shoulder or across the back, or even in the knee. You'd have to be careful not to sprain your wrist as you swung it at them.
Or you could throw it at them, or drop it on their foot. I'm a bit worried that I might drop mine one day. I don't fancy a broken foot. If it misses my foot it'll break the floor.
The knife would be best for its dangerousness but you'd have to go right up close to them to attact them. You want to keep your distance really. And it's messy if you do attack them with it. blood everywhere. You can't just knock them out with a knife, if you do attack them with it you risk bleeding them to death and I wouldn't want to do that. Don't want a dead person in my kitchen.
Meat tenderiser is probably best - light enough to swing, hard enough to cause plenty of pain and possibly unconsciousness, but not so heavy that it would kill too easily.