The important thing is to get the TSA locks that have a safety alert. That is a red collar or dot that shows up on the lock when it has been opened with the TSA key. This way you know they have been in there as soon as you pick up the bag.

This alone is an important feature in preventing theft by TSA. Ordinary TSA locks without the safety alert only facilitate theft by TSA. They open your bag with their keys in the name of security, go through them and then take whatever they like. Obviously, they will not place a TSA ticket in your bag when it has been thusly pilfered.

I recommend colorful zip ties. Don't use black. They have black spares with which they will replace your zip ties. Use a gaudy neon color. They will most likely not have the color on hand. The zip tie acts like a seal that must be broken.

You can also put tape around the entire length of the zipper. That makes it too much hassle for quick thieves and is very obvious if it's missing.

Till