I was wondering what is the difference between 1) TTN Lns with AWS integration and 2) AWS IoT Core with Lns only?

Why would you use the one over the other if you have your own gateways? With own gateways, is 2) better?

As always it depends on what you want.

TTN provides coverage in many places without the requirement of installing your own gateway. TTN has this awesome commercial, if you have issues you can ask questions on the forum or if you use a commercial instance use support. There is a lot of LoRaWAN experience on the forum, however only available for TTN use, if you go AWS only you’ll need to find support elsewhere.
And if you connect to TTN you also provide coverage to the community. So there is the feel good factor as well.