which one to maintain the LDP session between LDP neighbors?

The LDP session protection feature keeps the LDP peer session up by means of targeted discovery following the loss of link discovery with a peer.
• LDP initiates backup targeted hellos automatically for neighbors for which primary link adjacencies already exist.

To enable the LDP session protection feature for keeping the LDP peer session up by means of
targeted discovery following the loss of link discovery with a peer, use the “session protection” command in MPLS LDP configuration mode in Cisco IOS XR Software.

On Cisco IOS and IOS XE Software, the similar command to enable LDP session protection is the mpls ldp session protection global configuration command.