The iPhone 11 Pro Max and iPhone XS Max share many features: Face ID, True Tone display, 4k video capability, and more.
They even sell for the same starting price: $1099 for 64 GB. Apple is no longer carrying the iPhone XS Max, but you can find it for the same price at Best Buy.
If you already have an iPhone XS Max, these are all pieces to consider before you switch. If you're buying a new phone, you won't necessarily save any money going for the older model, so you might as well get an upgraded camera and better battery life with an iPhone 11 Pro Max.
Before you decide to upgrade, remember to check the trade-in value of your old phone.